Jack Campbell

"Right, you're the control, and if that fails, I'm the damage."

- Jack Campbell to Elliot Swann, shortly after arriving on Mars

Jack Campbell is a major character in Doom 3. He serves the UAC Board of Directors, Elliot Swann, as a subordinate and a personal bodyguard.

Background
Not much is known about Campbell's background. However, he appears to be a former military personnel (as he is equipped with the same body armor issued by the Marines) who works for the Union Aerospace Corporation under supervision by Counselor Elliot Swann. His prior experience in combat has earned him the duty to escort Swann as his bodyguard in order to protect him from any possible threats or accidents that has been plaguing Mars as of late. Campbell is a quiet and self-reserved individual, as he is more focused on fulfilling his own given task of escorting Swann and obeying his orders without question. If he has his own opinions, he does not share it, as it is not his place to do so.

Doom 3
Campbell is first seen arriving to Mars City from a Phantom Dropship, wielding a large briefcase while chaperoning Counselor Swann. Swann, expressing annoyance that his arrival on Mars largely results from Dr. Malcolm Betruger, ensures that the elderly doctor must meets to his own demands. Campbell concurs, and adds to Swann's point that if that is not the case, he will take more drastic action under Swann's behalf.

Campbell is later seen in a conference room in Mars City, standing next to Swann who engages in a heated discussion with Betruger in regards to the recent events that has been happening on Mars. Staying completely silent on the matter between the two men, he notices the recent Marine transfer he has seen earlier from the Dropship, eavesdropping on their conversation. Betruger then departs from the conference room, followed by Swann and Campbell.

Shortly after the invasion, Campbell is seen in the Administration Complex, standing next to Swann, who engages in another argument with Betruger through a telecam about the predicament they are in. Realizing that Betruger refuses to meet up to his own demands, Swann turns off the telecam and turns towards Campbell, which Campbell acknowledges Swann's approval to execute "Plan B". He opens his briefcase to unleash the BFG9000.

Swann's plan is later revealed to make every attempts necessary to shut off all communications on Mars from Earth, while having Campbell to safely escort him throughout the base by fending off demons with his weapon and to sustain the invasion. He is seen helping Swann locate the transmission card from the fallen Bravo Team in Enpro Plant, and sabotaging the main communication relay in the Communications Room before heading off to the Delta Complex.

Eventually, both Swann and Campbell become ambushed by Sergeant Thomas Kelly, who has converted to the demon's side. Swann is critically injured as a result, forcing Campbell to leave him behind and hunt down the former sergeant himself. Campbell later gets overwhelmed by Kelly. Mortally wounded, the last thing Campbell does is to ask the approaching Marine to stop Sarge and warn him that he has acquired his BFG9000, before expiring.

Trivia

 * On some levels when the player is already aware of Campbell's presence, they can hear BFG shots accompanied by the cries of enemies dying nearby. Shortly before the player fights the Vagary boss in Alpha Labs Sector 4, he can be seen firing a BFG shot to destroy a couple of Trites surrounding them, before leaving.