Jack Campbell is UAC Counselor Elliot Swann's trusted bodyguard and loyal henchman. He wields the most powerful weapon in Doom 3: the BFG 9000.
Campbell is seen with Elliot Swann in some of the cutscenes, although during gameplay the player gets a chance to watch him blast a group of Trites through a window using the BFG 9000 at very end of Alpha Labs Sector 4, just before first contact of Vagary.
Campbell considers himself to be the "damage" part of "damage control" (Swann being the "control"). Wielding his BFG 9000, Jack Campbell is the bodyguard of Counselor Swann and protects him while they attempt to escape the demon invasion. Campbell does not have a high opinion of Doctor Malcolm Betruger, who he considers to be stubborn and does not think that he will bend in to any of UAC's demands and that Swann's mission has no point.
While seen mostly just in cutscenes, he is seen ingame several times: In the pre-invasion Mars City after the cutscene involving Swann and Betruger he can be seen walking out of a door after Swann; in the Administration Complex's Global Network Terminal with Swann; running down a hallway with Swann in Alpha Labs Sector 1 while the player battles some Maggots in the Hydrocon Chamber; again when he kills some Trites at the end of Alpha Labs Sector 4; in the Communications Room where he uses the BFG to destroy all the computer equipment; and for the final time when he encounters the Marine. He is badly wounded, and advises the Marine to watch out for Sergeant Kelly (Now Sabaoth), who took his BFG 9000. He dies shortly afterwards muttering the words: "Sarge... find him... you gotta find him... my gun... he's got my gun...".
- If you kill Campbell when he is holding his BFG suitcase, or when he is holding the BFG, his body cannot be gibbed up, and you can obtain his BFG 9000. However, you can gib him in the CPU complex.
- Considering that he wears Marine armor and is trained to use the BFG 9000, Campbell is probably ex-military.
- This is confirmed by the Making of Doom 3 book.