Paranoid Marine
From Halopedia, the Halo wiki
This UNSC Marine was presumably a member of Fire Team Charlie deployed to what Captain Keyes thought was a Covenant weapons cache. In reality, the fire team was headed for a Flood Containment Facility.
This Marine was inserted into the swamp by Pelican Victor 933[1], along with Sergeant Johnson, Private Bisenti, Private Mendoza, and Private Jenkins. The squad rendezvoused with Captain Keyes, along with Privates Kappus and Riley, after discovering the remains of a dead Elite. After entering a large hall, the squad was ambushed and attacked by small, squidlike creatures. This Marine witnessed the death of almost his entire unit, and fled the battle.[1]
Long after the Flood had finished their massacre of the Marines and Covenant alike, [[Spartan-117] came across this Marine. The soldier was a wreck, firing at anything that moved with his pistol, and hollering about "monsters." It is unknown what happened to this Marine after the Chief encountered him, though he definitely died when Installation 04 was destroyed.
References
On Jenkins's helmet recording, a fourth unnamed Marine besides Johnson, Jenkins, Mendoza, and Bisenti can be seen on the dropship. During the Flood ambush, Keyes can be heard yelling at a Marine "Get back here Marine, that's an order!" It can be presumed that this is the Crazed Marine.
