Corporal Adrian Shephard is a 22-year old US Marine Corporal assigned to the Hazardous Environment Combat Unit from the Santego Military Base, Arizona, where he was trained by Drill Instructors Dwight T. Barnes and Sharpe, and the silent protagonist of Half-Life: Opposing Force. He is one of the men sent in the Black Mesa Research Facility to kill the Xen invaders and later silence the witnesses, especially a scientist named Gordon Freeman, as part of a classified mission. Early in the game, Shephard finds himself separated from his unit and ends up fighting for his life only, aided by fellow Marines scattered around the facility and Black Mesa employees.