Doom is a 1993 first-person shooter (FPS) developed by id Software for MS-DOS. Players assume the role of a Space Marine, known as Doomguy, fighting their way through hordes of invading demons from Hell. The first episode, comprising nine levels, was distributed free as shareware and played by around 15–20 million people within two years; the complete game, with two more episodes, was sold by mail order. An updated version with an additional episode and more difficult levels, The Ultimate Doom, was released in 1995 and sold at retail.
