Half-Life: Source

Half-Life is a 1998 first-person shooter (FPS) game developed by Valve Corporation and published by Sierra Studios for Windows. It was Valve's debut product and the first game in the Half-Life series. The player assumes the role of Gordon Freeman, a theoretical physicist who must escape from the Black Mesa Research Facility after it is overrun by aliens following a disastrous scientific experiment. Its gameplay consists of diverse combat, exploration and puzzles.