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 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.

With dropship Bravo 22 destroyed halfway through the op, Echo 419 escorting the Master Chief on a higher-priority mission, and what remained of the squad in no condition to assist, Waller and his remaining men waited on the island for extraction. It is possible that Foehammer flew back up through the tunnels and brought them back to Alpha base.

Survival
Sergeant Waller was not picked up to escort Captain Keyes to the weapons cache, as according to Halo: The Flood Captain Keyes and the squad were already ambushed when the Chief returned topside on the Silent Cartographer.

Death
It is unknown what happened to him after the Cartographer. It is possible that he was either evacuated back to Alpha Base to later fight the Covenant, and killed when Lt.Mckay destroyed the Truth and Reconciliation.

Trivia

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