Doom is a 1993 first-person shooter (FPS) video game developed by id Software for MS-DOS. It is considered one of the most significant and influential titles in video game history, for having helped to pioneer, along with the 1992 game Wolfenstein 3D, the now-ubiquitous FPS gameplay type, and has been frequently cited as one of the greatest video games of all time. The original game was divided into three nine-level episodes and was distributed via shareware and mail order. The Ultimate Doom, an updated version featuring a fourth episode, was released in 1995 and sold at retail.