Wolfenstein 3D is a first-person shooter video game developed by id Software and published by Apogee Software. Originally released on May 5, 1992, for the PC operating system DOS, the game was inspired by the 1980s Muse Software video games Castle Wolfenstein and Beyond Castle Wolfenstein. A promotional version of Wolfenstein 3D was released as shareware, which permitted it to be copied widely. The game was later ported to a wide range of computer systems and video game consoles. The shareware release contains one episode consisting of ten levels. The commercial release consists of three episodes, which include the shareware episode and two subsequent episodes. Later releases included a three-episode mission pack titled The Nocturnal Missions. The player assumes the role of a World War II Allied spy William "B.J." Blazkowicz, who is trying to escape from Castle Wolfenstein, a Nazi German prison. After the initial escape episode, Blazkowicz carries out a series of crucial missions against the Nazis. Wolfenstein 3D was a critical and commercial success. It is widely regarded as having helped popularize the genre on the PC and having established the basic run-and-gun archetype for many subsequent first-person shooter games.