From Halopedia, the Halo wiki
Alan Wray Tudyk (born March 16, 1971) is an American actor, best known for his roles as Hoban "Wash" Washburne on the space western TV series Firefly and Sonny in the film adaptation of Isaac Asimov's I, Robot.
Tudyk voices a UNSC Marine NPC in Halo 3. He also voices PFC Michael "Mickey" Crespo in Halo 3: ODST. In Hunt the Truth, Tudyk voices Captain Noah Reibach.