Doom is a series of first-person shooter video games developed by id Software. The series focuses on the exploits of an unnamed space marine operating under the auspices of Union Aerospace Corporation (UAC), who fights hordes of demons and the undead in order to survive. Doom is considered to be one of the pioneering first-person shooter games, introducing to IBM-compatible computers features such as 3D graphics, third-dimension spatiality, networked multiplayer gameplay, and support for player-created modifications with the Doom WAD format. Since the release of Doom in 1993, the series has spawned numerous sequels, expansion packs, and a film. Many credit it as starting the FPS genre. Since its debut, over 10 million copies of games in the Doom series have been sold.