Tristan has climbed through the ranks of the Brotherhood of Steel and finally attained the status of paladin, one of the highest ranks. He acts as an operation specialist, planning many of the offensives in defeating the Enclave in the Capital Wasteland.
Blood Brotherhood: Following the destruction of Adams Air Force Base, Tristan asks you to collect Super mutant blood samples, so the scribes can research and develop a weapon that can destroy the super mutant population once and for all.
Effects of player actions
He is the acting field commander of the Brotherhood forces in light of Sarah Lyons being unable to fight after the events at the purifier, and is in charge of all Brotherhood operations involving the player and Liberty Prime, the first mission in the main Broken Steel questline.
When you first encounter him in the Rockland Car Tunnel, he will sometimes be unarmed and in the "fist-fight" stance; however, pickpocketing will reveal that he is carrying a plasma rifle and simply has no ammunition. He will find some ammunition by himself after Liberty Prime kills the first Enclave soldiers, but you can also reverse-pickpocket him some microfusion cells while in the tunnel which will make him fully operational after loading the next screen.
xbox360 If Tristan suffers a crippled leg during the assault on the Communications station, he will spend the rest of the game crippled never bothering to heal it.