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.

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.