"Half-Life: Opposing Force" is the first expansion for Half-Life, which was made by Gearbox Software instead of Valve. It was released on November 1, 1999. Half-Life: Opposing Force happens during the same time as Half-Life and in the same setting. In the expansion, you play as Adrian Shepard, a United States marine. He was sent to Black Mesa, and must escape after the helicopter he was riding was shot down.