Thomas Kelly

Sergeant Kelly is one of the first characters the player meets in Doom 3. He is the ranking non-commissioned officer on the Mars Base, and orders the player to Mars City Underground to find a missing scientist.

His role on the game is significant, as to command the doomguy with different orders than those from Swann, he creates a contradiction in what should the doomguy do. Eventually however, Swann's orders are shown to be the best ones as they avoided a possible hell invasion on Earth.

After the demon invasion, Sergeant Kelly makes only one more personal appearance, as Sabaoth, a mutated freak with tank treds for legs, armed with a mechanical claw and Jack Campbell's BFG 9000. He is the third boss out of four in Doom 3 and presents a formidable challenge.