The AWOL Marine was a UNSC Marine, originally a member of Fire Team Charlie, deployed to what was thought to be a Covenant weapons cache. In reality, the fire team was headed for a Flood Containment Facility.
The unknown Marine was inserted into the swamp by a Pelican, along with Staff Sergeant Avery Johnson, Privates Bisenti, Mendoza, and PFC Wallace Jenkins. The squad met up with Captain Jacob Keyes, along with Privates Kappus and Riley, after discovering the remains of a dead Sangheili. After entering the facility and taking a lift to its lower levels, the group of marines and Captain Keyes enter a large hall, with four doors. The squad is then ambushed and attacked by "small, squid-like creatures". This Marine witnessed the death of almost his entire unit, and fled the battle, successfully hiding from the Flood.
Long after the Flood had finished their massacre of Marines and Covenant alike, John-117 came across this Marine. By that time, the Marine was a psychological wreck, firing at anything that moved with his M6D pistol. The Marine made no distinction between UNSC, Covenant, and Flood; his severe mental trauma had made him hostile to anyone and anything besides himself.
In Halo: The Flood, John-117 came through a door and was immediately shot by the Marine, his shields taking a substantial hit from the powerful pistol round. John closed in and confiscated the weapon, reprimanding the Marine for firing on an ally so freely. The Marine stood up and briefly tried to take the pistol back, but the Spartan effortlessly pushed the Marine back down. None of John's efforts to question the Marine about the status or location of Captain Keyes or the rest of the Marine's unit gained any useful information; the Marine gave rambling, incoherent responses and panicked shouts. The Marine yelled for John to "Find your own hiding place!" and said he could "hear them". John then ordered the Marine to be more careful with his shots and conserve ammunition, and to head for the surface. The Marine didn't acknowledge the order, but merely accepted the M6D, curled into a fetal position, whimpered, then fell silent.
It is unknown what happened to the Marine after the encounter, though most plausible scenario is that he was killed by the Flood, for if the player attempts to return to his position later in the level after encountering the Flood, the door leading to the Marine's position is damaged and will not open, and looks as if it had been smashed from the inside by something quite strong. It is also possible that he committed suicide. If neither of these events happened, he surely would have been killed by the destruction of Installation 04. However, it is very unlikely that, with the ammunition and weaponry he had on his person or could have found, along with the lack of suitable armor (similar to John-117's Mjolnir Powered Assault Armor) to better defend himself that he would have survived that long.
- "Stay back! Stay back, you're not turning me into one of those things!"
- "I'll blow your brains out! Get away from me!"
- "Gaaaaahh! Aaaaahh! Don't touch me, you freaks, I won't be like you, I'll die first!"
- "Find your own hiding place, the monsters are everywhere!"
- "Play dead! That's what I did... played dead. They took the live ones... Oh, God, I can still hear them!"
- (sob) "Monsters..."
- "Ahhhhhh! Ahhhhaaahhh..."
- "Just leave me alooooone!"
- "Sarge? Mendoza? Bisenti? All gone...the things took them, away, away, away, they went away... "(mumbles and cries) "They're gone! Get it? Gone!"
- "They won't get me! Oh God... oh God I don't want to be like them, please, please no, please nooo..."
- His fate is unknown, as the room he was in locks after John comes back out. However, it is possible and rumored that he proceeded to the structure's "basement," as later a human body is found on a flaming platform, and a pistol lies next to it.
- There was an idea for the Crazed Marine earlier in the development of 343 Guilty Spark. He would've stayed alive initially, but when the player walked a distance away from him, there was supposed to be a loud bang. If the player returned, they would find him dead on the floor. This was revealed by Joseph Staten on the Halo 3 Legendary Edition bonus disk.
- Strangely he says that the Flood Infection Forms ignored his false dead body despite the case that the Flood would consume either living or dead beings. However, they also ignored a dead Sangheili (seen in the cutscene in the same level), so it is possible that the pre-Coordinated stage Flood were purposely leaving some dead bodies in order to lure more victims into their trap.
- As a homage to this Marine in Halo: Combat Evolved, the Halo 3 Suicidal Marine is voiced by the same person, and features similar mannerisms to the original. He can be seen on the level Floodgate.
- In Halo: The Flood, John-117 was actually shot by the Crazed Marine, but he immediately took the M6D from the Marine and tried to talk sense into him before he crawled back into a fetal position.
- You can kill him with one shot by any weapon.
- Reloading sounds can be heard, but he doesn't appear to be reloading his pistol.
- You may hear him shooting after you leave him (but staying in the same room).
- The AWOL Marine is an example of an Ambient A.I.
- The Marine does not register on John's HUD reticle as an enemy as it does not turn red; it simply remains blue. Some players still dub him as a Human enemy.
- You cannot move his body after he is killed, even with grenades.
- Even if you go behind the wall he is sitting against, he seems to be able to see you.
- He is the only Marine besides Sergeant Johnson to call the Marines by their name. All other Marines encountered in-game will not say another's name, rather calling their comrades "Marine."
- Suicidal Marine - Another Marine who lost his mind after battling the Flood, encountered by the player in Halo 3.
- Wounded Marine - A third Marine who became delusional after the attack of the Covenant at the Battle of Earth, encountered in Halo 3: ODST.
- Crazy Army Trooper - An Army trooper in Halo: Reach, gone crazy after multiple encounters with the Covenant at the Fall of Reach.