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 M6G 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.
- "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 up to the player in which, the player can end his misery for him or walk away and then the Marine shoots himself with his last bullet. Either way there is no way to save his life.
- Originally in Halo CE and CEA, the AWOL Marine would have infinite ammo and his fate was unknown. In SPV3, his suicide (which was originally cut) was restored and only has about one clip of bullets, save for his last one.
- 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."
- 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.