Waller

Gunnery Sergeant Waller was a Non-Commissioned Officer in the UNSC Marine Corps during the Human-Covenant War. He was in command of an Marine Shock Troop unit during the Battle of Installation 04 in September 2552.

Battle of Installation 04
Waller was one of the Marines stationed aboard the as part of Major Antonio Silva's and 1st Lt. Melissa McKay's ODST Infantry contingent. He made the random slipspace jump to Installation 04 along with the rest of his unit after the major defeat at Reach during the battle that took place there.

He was present when the Pillar of Autumn was boarded by units of the Covenant Navy during the opening phases of the Battle of Installation 04. He successfully escaped the ship, that later crash landed in a desert on the ring.

Presumably, he was part of the attack that took Alpha Base and later part of the convoy McKay made to transport supplies from the Autumn.

The Cartographer
He was one of the Marines in charge during the airborne assault, along with Sergeant Major Avery Johnson and Gunnery Sergeant Pete Stacker, on the Silent Cartographer.

He and his Marines came under heavy Covenant fire as soon as MCPO John-117 left them outside the Cartographer building, and most of the Marines were either killed or wounded in the skirmishes.

Survival
Gunnery Sergeant Waller was picked to go with Captain Jacob Keyes and Sergeant Major Johnson to find a hidden Covenant weapons cache, from intelligence given by a captured Sangheili Minor. During the investigation of the area, they were ambushed by the Flood when trying to get a radio signal for an immediate evac.

Captain Keyes, and all of the Marine Infantryman and Shock Troops inside of the facility were assimilated into the Flood during the ambush. However, the veteran Avery Johnson managed to escape the flood after fighting his way out of the building.

Though Waller was outside of the building, therefore he survived the Flood ambush, along with around 10 other Marines, from the containment building.

Death
It is unknown what happened to him after the Flood outbreak. It is possible that he was either evacuated back to Alpha Base to later fight the Covenant or that he was assimilated into a Flood Combat Form.

Trivia

 * Waller's single appearance is in Halo: The Flood, whereas in the game his role is filled by Pete Stacker in Halo: Combat Evolved.