Thomas Kelly

Sergeant Thomas Kelly is one of the first characters the player meets in Doom 3. He is at the top of the enlisted chain of command on the Mars Base (Marine HQ). Though he appears to be somewhat cold, he is very well respected for his duties and leadership. A former career military man, he only expects the best from his men. He gets easily agitated when one "slacks" on his efforts, and typically assigns slacking marines to the worst duties as punishment (such as being assigned to the solid waste facility). Kelly makes this very obvious when you first encounter him, as the first thing he says to you is: "Took your sweet time, marine?"

Fortunately, it's your first day so he shrugs it off and gives you your first assignment (allowing you no time to settle in due to the lack of troops). You must locate a scientist who is missing and never showed to his post (Dr. Ishii, Delta labs researcher) and bring safely him back to HQ. Sergeant Kelly then sends you on your way with a Sentry Bot to guide you (he remarks that he hopes you follow the Sentry better than you've followed orders so far).

Not long after you locate the missing scientist, the demonic outbreak occurs killing (and possessing) Dr. Ishii and along with almost everyone on the entire base. Sergeant Kelly, now in Delta Labs, orders all remaining marines to head back to HQ for further orders. You are the only marine to arrive at HQ alive.

When you approach the communications monitor, Sergeant Kelly appears on the screen. He seems both surprised and relieved to see you and gives you your next set of orders: Link up with Bravo team in order to send a distress call. His role in the game is significant: as he commands the Doomguy with orders different than those from Councilor Swann, he creates a conflict as to what the Doomguy should do. Eventually, however, Swann's orders are shown to be the best ones as they avoid a possible hell invasion on Earth. In any case, it doesn't really matter, since if the Doomguy doesn't contact the fleet, then Betruger does it himself.

After sending/canceling the transmission, the player is not contacted by Kelly again until he reaches Delta Labs. Kelly appears on a monitor and tells the player to meet him at Service Tunnel 1, but when the player gets there, Kelly is nowhere to be found (in fact, a trio of Cacodemons teleports in). After this, the player does not see or hear from Kelly again until the CPU Complex.

At some point during the game, Kelly is converted over to the demons' side. He ambushes Campbell and Swann in Delta Labs, gravely injuring Swann. Campbell chases after him, leaving Swann behind. The player encounters the wounded Swann, who warns him that Kelly has been turned. The player makes his way to the CPU complex where he finds Campbell, who has been ambushed and mortally wounded by Kelly. Before expiring, Campbell tells the player that Kelly has his gun. At this point, Kelly contacts the player and taunts him saying: "I killed that pathetic bodyguard, and now I shall kill you."

In the next level, the player comes face-to-face with Kelly, who has been transformed into a hideous tank-like monstrosity called Sabaoth. The player has no choice but to fight and kill his former commanding officer. After you defeat Sabaoth, you are rewarded with Campbell's BFG 9000.

The reason for Kelly's "incident" still remains uncertain. While some affirm he was working with Betruger and the demons since the beginning (substantiated by the fact that he insisted in contacting the Earth armada to bring them to Mars, maybe knowing it would be taken over by the demons), others think he was captured, mind-enslaved and transformed by Betruger to serve him, and that his zealous attempts at contacting the fleet to get reinforcements were simply basic military logic (realizing that the battle is lost without reinforcements). Furthermore, Kelly would have no reason for being in league with Betruger before the invasion since he never made a trip into Hell.

It should be noted that Kelly's appearance and behavior are subtly different once the player reaches Delta Labs (his facial complexion is somewhat paler and he seems almost disappointed that the player is still alive), suggesting that some alteration has occurred to him by that point in the game. It should also be noted that if the player chooses not to contact the fleet, Kelly will angrily start to order the player to send the transmission only to be inexplicably cut off. This might be the point at which Kelly was attacked and converted over to Betruger's side.

Bugs

 * In the French version of Doom 3, Sarge's "final warning" is in English.