|Catherine Elizabeth Halsey|
Date of birth
|Physical and combat information|
170.2 centimetres (5 ft 7.0 in)
117 pounds (53 kg)
M6 sidearm, unknown model
|Chronological and political information|
Catherine Elizabeth Halsey, MD, PhD, (SN: CC-409871) was a praised scientist and former employee turned prisoner of the Office of Naval Intelligence, best known as the creator of the SPARTAN-II Program and MJOLNIR Powered Assault Armor. Despite being a civilian, she held considerable authority within ONI and commanded considerable respect from many military figures. As she grew older, Halsey began to feel guilt for condemning her SPARTANs to a life of warfare which took their lives, and took various extreme measures to protect her remaining SPARTANs, even going against the military law to do so - a choice which would result in her eventual arrest by ONI's Kilo-Five in 2553. As of 2558 when Admiral Osman had ordered the execution of Catherine, the latter escaped the assassination attempt and defected to the alien hegemony, the Covenant Remnant.
Catherine Elizabeth Halsey was born on Endymion on March 19th, 2492. Her childhood would give a glimpse of what would be a promising career. She was "smarter than her parents, always reading, talking, learning, and eager to share her knowledge with anyone who would listen." She was sent to Endymion Gifted which was an elite academy where she continued to push the standards of education. In 2501, her exceptional performance in school afforded her a trip to Circumstance by the Dean of Biological Science at Koletre-Browning University. The Dean paid for her education until 2507. By this point, at 15 years old, Dr. Halsey was already writing her second Doctoral Thesis paper, in which she discussed archaic line commands. It is also known that at some time in her early life, she supervised the creation of the template for third-generation Smart artificial intelligences. She was Vice Admiral Ysionris Jeromi's star pupil as well. ONI recruited her in 2510 as a civilian consultant and brought her to Reach. In August of that year, Halsey purchased a small, hardback journal in a shop on Reach, near the base she was stationed in. Halsey used the journal as a medium through which to express her thoughts and concerns, as well as pen important research notes, and would do so for another forty-two years, until she abandoned it during her escape from Sword Base. The journal was later recovered by ONI in 2553, and was designated top secret.
During their survey travels for the Spartan-II candidates, Halsey grew attached to Jacob Keyes. The two were involved in a romantic relationship in the early 2520s, and in 2525, Halsey gave birth to Miranda and raised her for a few years, when on July 12, 2531, Miranda's father agreed to take her in, raising her on Luna. Halsey would later have a falling-out with Miranda, who would later change her legal name to her father's and refuse to speak to Halsey for several years.
- Main article: SPARTAN-II Program
- “This boy could be more useful to the UNSC than a fleet of destroyers, a thousand Junior Grade Lieutenants -- or even me. In the end, the child may be the only thing that makes any difference.”— Catherine Halsey speaking to Lt. Jr. Grade Jacob Keyes, referring to John-117.
Dr. Halsey served as a scientific adviser for the Office of Naval Intelligence from 2515 to 2522, when she was made chief scientist. She made huge contributions to many ONI Section III projects, including the creation and deployment of AI constructs. She created and initiated the SPARTAN-II project, and designed the MJOLNIR armor system. These scientific advancements all proved to be important breakthroughs for the UNSC, as they were ultimately responsible for ensuring the survival of mankind.
In 2517, at the age of 25, Dr. Halsey helmed the SPARTAN-II Program; SPARTAN-II would create a new generation of supersoldiers based upon the earlier work of the ORION Project using abducted children. Establishing a set of rigorous genetic criteria to screen potential candidates, she identified 150 children for the program, but ONI would only give her enough funding to train 75. Thus Halsey made arrangements to meet each of the candidates in order to determine who her 75 candidates would be. At her request, Junior Lieutenant Jacob Keyes accompanied her during the interview of John-117. Upon choosing her candidates, she then had the children abducted from their homes and brought to the planet Reach for training. The 'recruited' children were replaced with flash clones, which ultimately died within a few years from various neurological and physiological diseases due to complications arising from the unperfected flash cloning process.
With the assistance of Chief Petty Officer Franklin Mendez and the dumb AI, Déjà, Halsey put her budding Spartans through a rigorous programme of physical training, military indoctrination and advanced tactics, supervising their augmentation procedures, combat training, and education, and monitoring the effects the training had on the children.
Halsey kept in close contact with her Spartans throughout their lives, from her base under Reach. Tellingly, she was always able to tell them apart from each other even under half a ton of MJOLNIR battle armor, an ability honed from years of familiarity which her Spartans found annoying. Dr. Halsey always used their first names, never their ranks or Spartan tags. She had a huge amount of respect for, and from, the Spartans; as their only mother figure, she commanded absolute obedience from her Spartans. Accordingly, she was also privy to the Spartans' closely held secrets, having taught many to them as children, such as the security code, Oly Oly Oxen Free.
Involvement during Human-Covenant warEdit
Battle of HarvestEdit
- Main article: First Battle of Harvest
After first contact with the Covenant, Dr. Halsey, under the pseudonym 'Charlie Hotel', accessed the data archive of LCDR al-Cygni's ONI Sloop, the Walk of Shame. During Dr. Halsey's investigation, she accessed the last conversations of the A.I. Mack in order to discover more about the Battle of Harvest.
- Main article: Raid on the Third Fleet of Glorious Consequence
In 2544, Halsey was captured by a Covenant Fleet during the Battle of Miridem while being transported in a cryo tube. A team of Spartan-IIs, consisting of John-117, Kelly-087, Frederic-104, Solomon-069, and Arthur-079 were sent to rescue her with Open Frame 92/Extra-Vehicular Activity vehicles. Knowing Halsey's value to both the UNSC and the Covenant, Luro 'Taralumee, the Covenant Fleet master, planted decoys in several CCS-class battlecruisers.
Solomon was killed by one of the decoys, which turned out to be an Antimatter Charge giving off a false signal. Arthur was also crushed between two cruisers while covering Kelly-087 from Seraph fire. John, Kelly and Fred eventually located the ship Halsey was on and engaged a large number of Covenant forces. However, Fred and Kelly were separated during the fight, leading John to believe they had been killed. Nevertheless, John finally reached Halsey and rescued her from her cryo pod, but they were stopped by then-Major Thel 'Lodamee. Halsey then watched as John fought the Elite in an Energy Sword duel. However, the Fleet Master in command of the Covenant Fleet detached the section of the ship they were in, retrieving Thel mid-fight using a Gravity lift, and jumped into Slipspace.
Halsey and John soon made it to a Covenant escape pod, but were engaged by multiple Seraphs. Halsey was visibly frustrated at the slow speed of the pod, going so far as asking John to take out the Seraphs with just his assault rifle. They were soon rescued by Fred and Kelly, who had captured a Seraph fighter. They then linked up with the UNSC prowler that had deployed the SPARTANs. Later, on board the Prowler, Halsey comforted John as he swore not to lose another Spartan.
Fall of ReachEdit
- Main article: Fall of Reach
On July 26, 2552, Halsey was working under ONI's Sword Base when it came under attack by a Covenant corvette. After the destruction of the corvette, she called Noble Team to her laboratory for a debrief, where she learned of the death of her colleague, Laszlo Sorvad, who had been stabbed through the abdomen by an Elite Zealot reconnaissance team. After arguing with Carter-A259 over Noble's failure to apprehend the Elites and Catherine-B320's attempted access of Dr. Sorvad's restricted files, she learned of the nature of Sorvad's "latchkey" discovery, a way to decipher data found in an underground Forerunner facility beneath Sword Base. After dismissing Noble Team, she began the decryption process of the "Latchkey" data in the Forerunner complex.
On August 3, Halsey split Cortana into two, assigning her "copy" to work on the decryption of the Forerunner data in the underground facility below Sword Base, while her other half would prepare for the Spartans' mission; Operation: RED FLAG. When the UNSC Iroquois arrived at Reach from Sigma Octanus on August 12, Halsey visited the ship. During her visit, Captain Keyes came to see her, and they discussed their daughter Miranda, the Keyes Loop, the Spartans and Operation RED FLAG. Later in the day, she visited Camp Hathcock to see John-117 after his debriefing. On August 27, she met most of the remaining SPARTAN-IIs at the FLEETCOM military complex in the briefing for RED FLAG, it was sometime after this that Halsey was listed as KIA, probably after the glassing of Sword base.Later, Noble returned after receiving orders to destroy Sword Base and all sensitive data. Halsey once again called Noble Team to her, revealing Noble's true orders to them: to transport a package containing "mankind's best chance for survival" to the Halcyon-class light cruiser UNSC Pillar of Autumn,which was holding position in the Aszod ship breaking yards. After Noble successfully defended her lab while she prepared the package, she entrusted Noble 6 with the package: a fragment of the AI Cortana, now uploaded with the information from the Forerunner facility. Once she made certain that Noble Six would deliver Cortana to the Autumn, she left for CASTLE Base under the escort of Jun-A266 while the remaining Noble Team members delivered the package to the Autumn.
Dr. Halsey then continued working in ONI's CASTLE Base. She volunteered to remain behind to ensure that all UNSC technology was secured from possible capture. She initiated Operation: WHITE GLOVE, eventually destroying several AIs (including Cortana's "older sister" Kalmiya) to keep the Covenant from accessing UNSC databases. With the expectation that the Covenant would glass the planet, and the knowledge that even if they didn't, she would be facing an entire army of Covenant ground forces, Halsey was prepared to sacrifice her work.
However, this changed when Spartans Fred-104, Kelly-087, Vinh-030, Isaac-039, and Will-043 appeared at the entrance to CASTLE Base. With the firepower to potentially fight their way out, surviving CASTLE Base's destruction became viable. She gave emergency aid to the Spartans for their injuries, but a data anomaly detected by her accompanying AI, Kalmiya, attracted Dr. Halsey's attention.
The data had been accessed by Araqiel, an AI that worked for Colonel Ackerson, one of Dr. Halsey's main competitors within ONI. After tracing the data access, Dr. Halsey stumbled across the AI, left behind by its master. Araqiel then threatened her, going as far as to tell her he would fill the room with poison, and that she would be reported. In response, Halsey typed in archaic line commands - the base code undergirding all AI functions which she had been instrumental in writing - to access his code directory and personal fail-safe, erasing Araqiel from existence. After he was destroyed, she pilfered through Ackerson's files, discovering a number of things including the location of Onyx, evidence of the SPARTAN-III program and a map of the mining tunnels CASTLE Base had been built upon. The latter particularly interested the Doctor as the file had been classified at X-Ray level, making the file abnormally important for an ancient geographical survey. Halsey thus deduced that there was something of importance under the mountain, and that it could be accessed through the mining tunnels under CASTLE Base.
Assuming that at the very least these maps provided a backdoor, she ordered her Spartans out of the base and into the mineshafts. She then triggered CASTLE Base's self-destruct mechanism and activated the fail-safe on Kalmiya. Together with her Spartans, Halsey evacuated CASTLE Base, moving deeper into the shafts below.
Over the course of the next five days, the Spartans and Dr Halsey searched the mines, looking for either an exit or what Dr. Halsey would dub "the most important discovery of the millennium". On the fifth day, Fred discovered an entrance into a large Forerunner structure, and within, the Forerunner Crystal. However, in acquiring of the crystal, they inadvertently released a spike of neutrino radiation, drawing large numbers of Covenant forces directly to their location.
Following a Covenant attack, Halsey and her team retreated into a hallway and were forced to seal off the entrance. Soon after, contact with Isaac and Vinh (who had volunteered to buy time for the others) was lost, and they were presumed dead. They quickly discovered that the hallway was a dead end, and Halsey and the surviving Spartans remained stranded at this location for some time.
Days later, a group of Spartans, including John-117, rescued Dr. Halsey and the remaining Spartans and evacuated them from Reach to the captured Covenant ship, Ascendant Justice.
Dr. Halsey later saw the importance of destroying the Forerunner Crystal after it caused a Slipspace anomaly that nearly resulted in the destruction of the Ascendant Justice. After escaping Reach, the group fled to the asteroid belt that the Spartan's first mission had been in. While there, she stole the rebel governor's spacecraft and, along with Kelly-087, whom she had sedated, escaped into Slipspace. When asked by Admiral Whitcomb as to the reasons for her actions, she gave a simple UNSC code "Three-Nine-Two," which meant that she was on a high priority mission. She entrusted the Forerunner Crystal to Corporal Locklear, telling him to keep it safe, hidden, and to do whatever it took to keep it from falling into enemy hands, as the Covenant would be able to go a hundred times faster in Slipspace should they obtain the Crystal. Locklear destroyed the crystal using an explosive, killing himself in the process. Despite his efforts, however, the Covenant managed to procure several slivers of the Crystal.
In the aftermath of the battle, she was presumed dead by the Office of Naval Intelligence and honoured along with other ONI personnel on a plaque at the ONI Alpha Site. It can be assumed the SPARTANs and Johnson neglected to report her retrieval from CASTLE Base then her following kidnap of Kelly and apparent desertion from the UNSC. Another possibility is that her name was added to the wall after the Battle of Reach but before the SPARTANs returned to Earth. It could also be that ONI did not want anyone to know that she had kidnapped Kelly, so they covered up the incident by saying she had died.
Battle of OnyxEdit
- Main article: Battle of Onyx
Dr. Halsey and Kelly eventually arrived at Onyx, while reuniting with SCPO Mendez and eventually her remaining SPARTAN-IIs and the SPARTAN-IIIs. She helped decipher the mystery of the planet. At first, she tried to maintain secrecy about her intentions out of habit, until Kurt-051 confronted her about it. She admitted that she was not actually looking for weapons, but rather the secret Forerunner Shield World, which she believed to be equivalent to a bomb shelter, and would be capable of keeping the remaining Spartans safe to evade the current war and let them live to fight another day. Her relative expertise with Forerunner technology was vital to the survival of the UNSC forces on the planet. At the end of the battle, she, along with Mendez, Blue Team, and the SPARTAN-III survivors, found herself inside the Shield World, which she believed was actually a Micro Dyson Sphere.
Escape from Shield WorldEdit
In Halo: Glasslands, the story is continued, finding that for several days, possibly weeks, she is stuck inside the shield world, with Blue Team, Chief Mendez, and the last of the SPARTAN-IIIs, until she is rescued by ONI. During the time she was trapped inside the Dyson sphere she translates many Forerunner symbols, in the hope of finding Lucy-B091, who went missing shortly after they began to explore a Forerunner structure inside the Micro Dyson Sphere. Several days later, Lucy returns with a Huragok named Prone to Drift who showed her how to get back to her team. Dr. Halsey then starts asking Prone several questions as to where they are, and how to get a message out to other humans outside the sphere. Prone states that he cannot let her do that because there is an unknown entity (presumably a human ship) outside the Micro Dyson Sphere, and he refuses to give Halsey access to the communications until he knows it's safe. After an unsuccessful attempt to persuade Prone to give her access to the comms, Dr. Halsey decides to ignore him and tries to access the communications system herself but before she can touch the controls Prone slaps her hand away, stating again that he cannot allow her access. The slap enrages Dr. Halsey and she starts to yell and threaten Prone, who is forced into a corner trying to protect himself. Lucy-B091 pulls Halsey back and punches her in Prone's defence. After much talk between the humans, Lucy speaks to Prone and convinces him that it is safe outside the Dyson Sphere, and Prone lets Dr. Halsey send a message outside the Dyson Sphere. The message is received by ONI operatives, who then relay the message to Margaret Parangosky, the head of ONI, who sends a message to Dr. Halsey requesting the Huragok bring the Dyson Sphere into normal space. In her transmissions to ONI while the Huragok prepare to bring the shield world into normal space, Dr. Halsey tells of the Forerunner artifacts that could be used by humankind such as the precision slip space technology. After the shield world is brought into normal space, Kilo-5 was sent in to arrest Halsey for the crimes she had committed (hijacking ships and kidnapping a Spartan). After her arrest, she was sent to the UNSC Infinity to work on upgrading the war ship. Afterwards, she was assigned to Ivanoff Research Station until at least 2554.
Halsey was later interrogated by an unknown individual regarding the SPARTAN-II Program. She defended the justifications for creating her SPARTANs, reminding her interrogator that they saved humanity. The interrogator then meticulously noted that the Spartan-IIs developed sociopathic tendencies. Halsey realized that her interrogator was looking for a reason to replace John-117, and insisted that the best of her Spartans was still alive and should not be underestimated.
Battle of RequiemEdit
- Main article: Second Battle of Requiem
- “-- One of the most dangerous assets we have in custody --”
Six months after the New Phoenix Incident, the UNSC Aladdin transported Dr. Halsey to the Infinity to examine a Forerunner artifact recovered by Fireteam Crimson during a mission on Requiem. The artifact had previously absorbed Dr. Henry Glassman into itself when he tried to study it. Halsey determined that the artifact is communing with Infinity's engines, which are based off Forerunner technology and something on the planet.
Some time later, Halsey began examining the artifact under the supervision of SPARTAN-IV Gabriel Thorne. She then received a communication from an unknown person, who informed her of the Promethean Knights. This led to Fireteam Majestic retrieving a package on Requiem. Upon examining it, the package let out a burst of energy and displayed images of New Phoenix. Noticing Captain Thomas Lasky and Commander Sarah Palmer sharing worried looks, Halsey confronted the former, accusing of having known the Prometheans' true nature. Lasky admitted that the UNSC has been aware that the Prometheans are ancient humans made into AIs. Halsey corrects that this Promethean is made from a person who lived in New Phoenix. Lasky expressed confusion, as these memories couldn't have gotten from Earth to Requiem. Thorne then abruptly left the room and Halsey realized that he had been staring at an image from the artifact.
Returning to the artifact, Halsey received another communication from the unknown individual, who, unknown to her, was Jul 'Mdama, the leader of the Covenant Remnant. 'Mdama then asked what she knew of The Librarian. Halsey accidentally repeated it out loud, causing Lasky and Palmer to become suspicious and discovered her secret communication. Lasky then ordered Palmer to arrest Halsey for withholding information.
Halsey was then moved to Lasky's ready room, her wrists cuffed. She defended that she did not give any information to her contact. Just as she criticized Palmer, Roland, the ship's AI informed the Captain that Thorne had been detected alive on Requiem.
After being placed in the brig, Roland asked her why she withheld the truth. She responded by using an AI override protocol on Roland to escape and gather what information the UNSC had on the Librarian, all of which was her own work, save for a debriefing of John-117, whom she apparently believed dead, after the New Phoenix Incident. She then got into communication with 'Mdama, offering her assistance to find the Librarian. However, Roland then managed to overcome the override and cut the communication and summoned security. Captain Lasky then confronted Dr. Halsey and planned to place her in cryo, but she slaps him in the face, accusing the Captain of withholding the truth about John-117's survival. Then suddenly, Promethean Knights began to teleport through the artifact onto the Infinity.
During the battle Lasky and Halsey are found by Palmer and are escorted back to the Infinity's bridge. However a lone Promethean Knight appears and takes Halsey hostage before teleporting back to Requiem. Some time after arrival she meets up with Jul 'Mdama at his base in the Librarian's chamber. After managing to deactivate the shield, which according to her required a 'more human touch', she runs into the beam which has formed in the Librarian's artifact and disappears. During this time however Osman as the new head of ONI has ordered Lasky to have Halsey eliminated should she ever be found again. Commander Sarah Palmer then assigns herself the task of eliminating Halsey, much to Lasky's protest. When Halsey entered the Shrine she came face to face with the The Librarian. The Librarian spoke about how Requiem's time was coming to an end, and how Halsey must accept her gift so as Humanity remains on the path to reclaiming the Mantle. The gift Halsey received was called the Janus Key, this artifact was indeed a map which showed every piece of Forerunner technology in the galaxy, this included all the Halo Installation locations as well as hidden Forerunner technology, that could propel Humanity into its next stage of technological supremacy. However, when Halsey accepted the gift she was launched back into Jul 'Mdama's clutches where he relieved Halsey of one piece of the Key, not realizing she had the second. Soon Thorne had gained entry into the Shrine and assassinated one of 'Mdama's bodyguards, while using Gek's cloaking device, Halsey quickly threw the second piece of the Key to Thorne just as Sarah Palmer arrives. Startled, 'Mdama summons the Promethean Knights to protect him, where Palmer attempts to assassinate Halsey but only managed a shot at her shoulder, 'Mdama soon escapes with the help of a Promethean Knight with Halsey as his hostage. An enraged Commander Palmer demands to know what Majestic was doing there, and when told their mission she questions why they would save a traitor, to which Thorne attempts to change her opinion by stating why had Halsey thrown him the Key if she was working with 'Mdama.
After Requiem is destroyed, Halsey is seen aboard 'Mdama's ship with her left arm amputated. Believing that both Palmer and Fireteam Majestic were sent to assassinate her, she offers to assist Jul 'Mdama in exchange for revenge against the UNSC.
Attack on ObanEdit
In July 2558, Halsey was able to convince Jul to attack the colony world of Oban in order to draw out the Infinity. Jul agreed, and a combined Covenant-Promethean force assaulted the planet. As planned, the ship was dispatched to Oban. With the Infinity in range, Halsey activated a Forerunner device to scramble the ship's Shaw-Fujikawa drive, preventing it from leaving a nearby star system. Jul's forces would wait on a nearby planet, hoping to retrieve the other half of the Janus Key from the UNSC. 
By 2589, Halsey had returned to humanity and on the 7th of July, she gave a Eulogy to SPARTAN-B312.
- “If people would just share things with me, I could solve all the world's problems.”— Dr. Catherine Halsey
Her intelligence is unquestionable as well as the loyalty and respect she receives from the majority of her comrades and her Spartans. However, as seen in Halo: First Strike, her judgment is not always correct, although bearing the guilt of the Spartan program, her sense of right and wrong has differed greatly. It is obvious that she truly cares about her Spartans. She has a notable fondness for classical music, especially Debussy, and often asks nearby AIs to play select pieces as she works.
What can be gleaned is that she preferred the company of AIs, and, although she may be angered easily at being mentally defeated, always appreciates the simplicity of them. None more than Cortana, who was actually created from a flash clone of her own brain. She is well-versed in Greek mythology.
Dr. Halsey carried extraordinary guilt because of the SPARTAN-II project, feeling that she had exploited the children and destroyed their lives, a feeling which was later passed to Cortana. Though she continued to support the Spartans and gained monumental prestige for her efforts, she also felt responsible for each one who died. She never could quite justify their exploitation as a "necessary sacrifice." She also had considerable respect for the Spartans, and addressed them by their first names (even with their armor on), which seemed to greatly annoy them.
Her feelings of guilt were made evident by the fact that she often referred mentally to "sacrificing the few to save the many," though this rarely worked to soothe her conscience. By the time she was rescued from Reach by the Ascendant Justice, she simply wanted to save as many lives as she could, believing that the war was not one that the UNSC could possibly win. While she knew that her own Spartans, the SPARTAN-IIs, couldn't be persuaded to turn from the war, she believed the SPARTAN-IIIs may not yet have been fully determined to win the war, and she set out to try and weaken their resolve to fight. When she was arrested Halsey allowed herself to be taken without any resistance due to her guilt.
Halo 4's prologue reveals that although Dr. Halsey carries the guilt of the SPARTAN-II project, she also sees them as the "next step" in the destiny of the human race.
- “Do not underestimate them. But most of all, do not underestimate... him.”— Dr. Catherine Halsey defending her SPARTAN's with special focus on John-117
Halsey also had somewhat of a unique relationship with John-117. Some of this may stem from him being the first subject she observed, but she had a great fondness for him and he was her favorite Spartan. Halsey told Cortana she considers him the luckiest and best of the Spartans and also apparently finds him attractive given her reaction to Cortana's comments on that. Halsey was responsible for John's first promotion to Squad Leader as a result of her acknowledging his leadership skills and suggesting it to Mendez. Halsey also had John's full trust and he always did his best to never undermine her authority.
Halsey decided to test her favorite SPARTAN's sense of ethics by handing over data concerning Avery Johnson and how his Boren's Syndrome made him immune to the Flood. She knew that if the data were handed over to ONI, Johnson would likely be killed and dissected in order to find a cure to the Flood infection. She estimated that there is a billion to one shot that they could have replicated Johnson's condition, but conversely ONI would do it to save Humanity from a greater foe. At first, John chose to sacrifice Johnson in order to try and save millions of people out of his duty to protect all of Humanity. However, John reconsidered and eventually destroyed the data due in part to the sacrifice of Vice Admiral Danforth Whitcomb and Lieutenant Elias Haverson, believing that one man could make a difference as opposed to sacrificing him for the greater good.
- Halsey is voiced by Jen Taylor, who also voices Cortana, reinforcing the connection between the two characters. This is also the case in Halo Legends, where Shelley Calene-Black voices both Halsey and Cortana. In Halo 4, Taylor also provides motion capture for Halsey.
- Catherine Halsey asked Kalmiya to play Mahler's Symphony No. 2 during her stay at CASTLE Base.
- In Halo: First Strike, it is stated that Dr. Halsey was not keen on losing, as seen when she kept losing at games of Twenty Questions and Simple Cipher with her training SPARTANs and soon quit playing.
- She had a knack for embarrassing the SPARTANs with the way she was able to tell them apart through subtle habits in their postures, despite their identical MJOLNIR armor, something no other non-SPARTAN was able to do.
- Unlike most others, Halsey never referred to the SPARTANs by their numerical designations, but by their names. However, she referred to Daisy-023 as "Twenty-Three" when trying to convince Daisy to return to the program.
- She had a bad habit of keeping a messy office and drinking cold coffee, tending to prepare the drink and then become distracted by work, only remembering it hours, sometimes days, later.
- Halsey served as a mentor to Professor Ellen Anders, though at some point prior to 2531, they apparently had a major falling out, as noted by Anders in the Halo Wars manual, saying "Why mention Halsey here? She hated me and I hated her."
- After the Fall of Reach, she was declared dead by the Office of Naval Intelligence (ONI), although no body was found. She was mentioned in a memorial plaque inside the ONI Alpha Site on Earth. This is because Admiral Parangosky, director of ONI, wanted Halsey to be thought dead, even though she was alive, and under arrest under charges of aiding the enemy, which was a result of her actions after the Fall of Reach, and throughout her life, mainly the way with which she acquired children for the SPARTAN-II program. Parangosky needed Halsey because of her technical expertise and knowledge of Forerunner technology, as ONI was building the most advanced UNSC warship ever built, the UNSC Infinity, which included a great deal of technology from the Forerunners.
- Two of Dr. Halsey's statements in The Package are references to similar statements made in the first two Halo games. She tells John-117 that she slept well "No thanks to their driving," which is echoed in Halo: Combat Evolved when he tells Cortana he slept well no thanks to her driving. She also tells John, "Don't make a girl a promise...if you know you can't keep it," which Cortana would tell him in Halo 2. Cortana would later say this quote in a different way to John in Halo 3 and Halo 4.
- Halsey's appearance changes drastically from The Package to Homecoming. In The Package, at which point she is aged fifty-two, she is inexplicably depicted as a fairly young woman with short, blond hair and no glasses. This may or may not have been reflected in the later appearance of Cortana, who was created from the replicated neural pathways of Dr. Halsey herself. Her appearance in Homecoming however, is slightly closer to her description from the books. It should be noted that various concepts in The Package, and Halo Legends in general, result from artistic license. Her appearance in Halo: Reach is much more in line with the description she received in the novels.
- Catherine Halsey is also a character in the 1943 novel, The Fountainhead by Ayn Rand, which is presumably where she got her name from. In the novel Halsey progresses into becoming an altruist, thinking of nothing other than the greater good of the majority. In this sense, she is an opposite of the Halsey of the Halo universe. Dr. Halsey begins by sacrificing the Spartans to buy the UNSC more time, but then changes her mind and does everything she can to save the Spartans, regardless of what happens to the rest of humanity.
- Dr. Halsey's personal journal is included in Halo: Reach's Limited and Legendary Editions, for which Bungie worked directly with Eric Nylund to make sure it is canonically accurate.
- In Halo: Reach, you can access Dr. Halsey's lab. To access this easter egg, you must play The Package on Legendary with at least two people. Using the Jetpack, find the hidden switch, activate it, and open a door on the far side of the map, releasing seven Sanghelli generals. After briefly waiting in this room, you will be transported to a long hallway. Walking down this hallway will bring you to her lab.
- The first five numbers on Halsey's security card (included in personal journal) are 10141. The sum of these numbers is another reference to "7." Interestingly, if you add together the numerical values of the letters in "Halsey" (e.g. A = 1, B = 2, etc.), they add up to 70.
- In Halo: Ghosts of Onyx, Halsey seems to know nothing about the SPARTAN-IIIs even though she met Noble Team on Reach, which consisted of SPARTAN-IIIs. The theft of Colonel James Ackerson's files in CASTLE Base allowed her to deduce the existence of a new version of Spartans.
- There is a discrepancy between sources as to whether Halsey's hair is blonde or black.
- Catherine Halsey was able to perfectly understand Jul 'Mdama, either because she understands Sangheili or had a translator device.
- She is the 4th person associated with the UNSC in the Halo universe to lose an arm. The third was SPARTAN-B320, the second was Captain Ponder, and the first was James-005. While she isn't the first normal human to lose an arm, she is the first to have it shown on screen.
- Halo 3 (Indirect mention only)
- Halo 3: ODST (Mentioned only)
- Halo: Reach
- Halo 4
- Halo: The Fall of Reach (First appearance)
- Halo: The Flood (Mentioned only)
- Halo: First Strike
- Halo: Ghosts of Onyx
- Halo: Contact Harvest (As "Charlie Hotel")
- Halo: The Cole Protocol
- Halo: Evolutions - Essential Tales of the Halo Universe
- Halo Legends
- Halo Wars: Genesis (Mentioned only)
- Halo: Glasslands
- Halo: The Thursday War
- Halo: Mortal Dictata (Mentioned only)
- Halo: Escalation
- ↑ 1.0 1.1 1.2 Halo 3: ODST - Alpha Site - ONI Memorial
- ↑ 2.0 2.1 2.2 Halo: First Strike, page 119
- ↑ 3.0 3.1 Halo 4: The Essential Visual Guide – page 14
- ↑ 4.0 4.1 4.2 Halo Waypoint: Catherine Elizabeth Halsey
- ↑ Halo Nation letter to Eric Nylund
- ↑ Halo: Ghosts of Onyx - page 177
- ↑ 7.0 7.1 Data Drop/HABA
- ↑ Halo: First Strike, page 123
- ↑ Halo: The Fall of Reach, page 235
- ↑ 10.0 10.1 Halo: First Strike, page 128
- ↑ Halo: The Fall of Reach, page 57
- ↑ 12.0 12.1 12.2 12.3 Halo: Reach - Dr. Halsey's personal journal
- ↑ Halo Graphic Novel, Page 122
- ↑ Halo: The Fall of Reach reissue Bonus Content
- ↑ Halo: First Strike, page 125
- ↑ Halo: First Strike pages 127-128
- ↑ Halo: Ghosts of Onyx
- ↑ Halo: Glasslands page 313
- ↑ Halo 4 – Composer Voice Recording
- ↑ Halo: Escalation Issue #1 - page 9
- ↑ Halo Escalation – Issue 13
- ↑ Halo: Ghosts of Onyx, page 148
- ↑ Halo: Ghosts of Onyx, page 157
- ↑ Halo: First Strike, pages 120-121
- ↑ Halo: First Strike, pages 242-246
- ↑ Halo: First Strike, pages 329-336
- ↑ Halo: Reach ViDoc: A Spartan Will Rise
- ↑ Halo: Legends credits
- ↑ Jen Taylor's Twitter account
- ↑ Halo: First Strike, page 123
- ↑ Halo: The Fall of Reach, page 230
- ↑ Halo: First Strike, pages 125-126
- ↑ Halo Wars manual, character profiles.
- ↑ Halo: Glasslands