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The player character and protagonist of Warhammer 40,000: Space Marine I and II, Captain (later Lieutenant) Demetrian Titus served as the commander of the Ultramarines' Second Company until the events of the first Space Marine game saw him taken into the custody of the Inquisition. After being released following his captivity, Titus, assuming that his chapter had expunged his records given the circumstances of his detainment, would join the Deathwatch as a Blackshield. A botched mission against the Tyranids would see him mortally wounded and turned into a Primaris Marine in order to survive. Afterwards, he would rejoin the Ultramarines (who had never forgotten him at all) with honors, though his absence would see him reinstated as a Lieutenant with Second Company having long been under new command.
He is known for his more lax attitude towards the Codex Astartes and his high resistance to the effects of the Warp and Chaos, the later of which has seen suspicion repeatedly cast upon him.