Waller
From Halopedia, the Halo wiki
Gunnery Sergeant Waller was a UNSC Marine and ODST. Waller was one of the soldiers stationed aboard the Pillar of Autumn as part of First Lieutenant Melissa McKay's unit. He made the jump to Installation 04 along with the rest of his unit when the ship crashed after being attacked by the Covenant.
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.
He was the ODST in charge during the amphibious assault on The Silent Cartographer. He and his men came under heavy Covenant attack as soon as the Master Chief left them outside the Silent Cartographer, and they were shot down, having failed to take cover.
Trivia
Waller's single appearance is in Halo: The Flood, whereas in the game his role is filled by Sergeant Stacker.
