T. Brooks was a Mars-Sec security guard stationed at a security office at the entrance to the Mars City Underground on Mars. He was responsible for permitting entry into the Underground. Brooks wore a standard Mars-Sec uniform and helmet with goggles.
When the player meets T. Brooks in Doom 3, he permits the player access to a security locker containing a pistol, armor, and a flashlight. He tests the radio connection, and warns the player not to get trigger-happy as civilians are working around the area.
He seems to be very well known in the Mars City Underground, as his email is found in almost every PDA of all the UAC employees in that area. This is most likely because he's the only one who can permit entry into the Underground.
- If you discharge your pistol when you first receive it, Brooks will flinch and yell at you to be careful.
- The Z-Sec of Brooks is actually another Z-Sec already positioned in his office, before the demon invasion. This can be seen by using the noclip cheat to enter Brook's office at the beginning of the level.