Oh, I know what the ladies like...
Born on Earth in the 25th century in the industrial section near Chicago, Avery’s family split up when he was just 6 years old and he was placed in the care of his aunt. She did her best to raise him, even clothing him in his cousin's best outfit to go to church. Her religious beliefs resonated deeply within Johnson and often made him question his own decision to kill other human beings, even long after her death.
When he was 19 years old, Avery joined the UNSC Marine Corps where he was to fight the Insurrection. In the Core, he applied for dozens of black operations and programs, the most famous of which would be the ORION Project. He was involved in many operations, one notable one was Operation: TREBUCHET. Here, when he was ordered to take a shot at a rebel, wearing a bomb-vest, he hesitated as he did not have a clear shot. Because of his hesitation, a civilian interfered which caused the bomb to explode, killing nearly all members of the Marine squad and 38 civilians. After the incident, Johnson came home and found his Aunt Marcille dead of natural causes, and soon went on a massive drinking binge. He started a brawl with bouncers at a Chicago club, and ended up sitting drunk by the door of the recruiting center until he was found by a UNSC Marine Corps recruiter; he was then reassigned to planet Harvest.
The Corps ain't payin' us by the hour!
Officially, his task on Harvest was to train the Colonial Militia, but this was a cover to create a covert anti-insurgency unit. But when they were hiding aboard a freighter to lure the rebels, they instead encountered the Kig-Yar in the first-ever encounter of the Covenant Empire. After a failed attempt to negotiate a peace treaty, Avery and the rest of the squad fought Jiralhanae Chieftain Maccabeus and his nephew Tartarus. He managed to repel the attacking Jiralhanae ship long enough for most of the population to evacuate after which he himself escaped.
We're even, long as we're only countin' today.
After the events on Harvest, goes out and fights in many battles until the Siege of Paris IV. During this battle against Covenant troops, Avery was forced to use a crate full of Covenant plasma grenades against them. This distraction gave Avery’s squad time to evacuate, but left Johnson exposed to twelve-hundred-rad cumulative dose of radiation, giving him, according to ONI medics, Boren's Syndrome.
He was later assigned to an orbital station above Reach, but was overrun and nearly killed during the Battle of Reach. When his situation seemed most dire, he was rescued by John-117 and Linda-058 and taken aboard the UNSC Pillar of Autumn. When the ship jumped away from the planet, it encountered a large ring-shaped world. This ring was filled with Covenant, and Avery soon found himself exploring a huge underground facility where they thought the Covenant kept their weapons. This facility was the old Forerunner research lab to investigate the Flood, which where unwittingly set free by the Covenant, the escaped Flood had killed all of the Covenant present. Avery and his squad encountered the bodies of several Sangheili and assumed friendly fire. Soon however, the Flood attacked Avery’s squad and mutated all members into Flood Combat Forms. The Flood also tried to take over Avery, but were unable to because of his Boren’s Syndrome. The syndrome had effectively given him immunity to the Flood, as radiation had scrambled his nervous system.
In truth however, Avery’s immunity to the Flood came from the experiments that were done on him in the ORION Program. Since this program was highly classified, ONI had fabricated this syndrome so they could give a reasonable explanation to Avery’s ability.
Dear Humanity; we regret being alien bastards.
When Avery returned to Earth safely, he was given time to rest and was debriefed on his experiences. Aboard Cairo Station, Avery was promoted to Sergeant Major and was awarded the Colonial Cross by Lord Terrence Hood for his actions on Halo. During the ceremony, a Covenant excavation fleet, led by the Prophet of Regret, arrived at Earth, sparking the Battle of Earth.
Aiding John-117 during the battle, they used the UNSC In Amber Clad to "piggy-back" unto the fleeing Covenant ship, and so discovering another Halo Array. Using their knowledge of the previous Halo, Avery was ordered to assist Miranda Keyes as she search for the Activation Index. In his searched he was captured by Thel 'Vadam and taken to High Chariety. Here he was kept until the Prophet of Truth ordered Tartarus to deliver them so their human touch could active the Halo Array.
After Thel 'Vadam and his squad had killed the Jiralhanae protecting Avery, he commandeered a Scarab in order to free Miranda from the Prophet. He was aided in this by Thel, who understood that firing of the ring would have killed them both equally. Approaching the Control Room where Miranda was to be forced to activate the Array, Thel was able to kill Tartarus, but not before he activated the ring. This activation was halted however, when the Index was removed. But 343 Guilty Spark explained that that set a fail-safe in motion, which who put all Arrays in 'stand-by mode' so they could allbe detonated remotely from The Ark.
The Ark was to be reached by a Portal, which was located in Kenya on Earth. The Covenant, aware of the location, went there in great numbers in order to excavate the Artifact. After the Portal was opened, Avery, with a half dozen Pelicans and John-117, helped secure a landing zone. In the time that the Covenant had been on the Ark, they had set up an impenetrable shield wall, which could at most be deactivated locally by the destruction of 3 power generators. While Thel 'Vadam and John-117 were sent to one generator each, Avery and his squad were sent to the third one, which apparently had been overrun with Jiralhanae, Mgalekgolo and Yanme'e forces, Avery failed in his attempts to deactivate the shield and was taken prisoner.
The Prophet of Truth attempted to use Johnson to activate the Ark, and set off the Halo array, but he only taunted the Jiralhanae, in particular a Chieftain, in hopes of angering the Brute to the point where he would kill him, and deny Truth the ability to activate the array. Miranda Keyes attempted to rescue him by crashing a Pelican through a large observatory window. Keyes was able to kill one brute, a Chieftain, and fatally wounded another, but was surrounded. Realizing what the Prophet of Truth wished to use them for, Johnson told her that she should kill them both so they could not be used. While Keyes hesitated, Truth shot her in the back with a Spiker, killing her instantly. The disheartened Johnson was then forced to activate the Array. Johnson was rescued by John-117 and Thel 'Vadam, along with a horde of Flood. After John-117 deactivated the array, the Flood turned on the three, and while Johnson managed to escape on Keyes' Pelican with her body, John and the Arbiter were knocked off by the Gravemind, forced to fight their way back through the Flood.
After it was discovered that a Halo was located within the Ark, a plan was developed to activate that ring and that ring alone, which would destroy the Flood on the Ark, including the Gravemind, ending their threat once and for all, while simultaneously sparing the rest of the life in the galaxy. While John-117 and Thel 'Vadam assaulted the outer layers of the Control Room, Johnson had taken a SPARTAN Laser and provided them with cover. When the two forces encountered each other at the door to the Control Room, they entered alongside 343 Guilty Spark, who had been inspecting the building of his new Installation. When it became clear to Spark however, that their intent was to destroy the ring by premature detonation, he attacked them, first shooting Avery fully in the body, taking out Thel and then engaging John. John then took Avery’s SPARTAN laser and defeated the AI construct.
Avery was mortally wounded and soon passed away, his final request was for John to "send him out with a bang". Following his wishes, John-117 left his body in the Control Room as the ring activated and tore itself apart. Johnson's body was disintegrated in the explosion while John and Thel took Avery's Warthog to escape. Johnson's death brought condolences from Cortana and Thel 'Vadam, whom Avery aided in his fight against Tartarus. On March 3, 2553, a picture of him was seen among the fallen on the Hillside Memorial.