Doom (typeset as DOOM in official documents) is a 1993 science fiction horror-themed first-person shooter video game by id Software.
It is considered to be one of the most significant and influential titles in the video game industry, having ushered in the popularity of the first-person shooter genre. The original game is divided into three nine-level episodes and distributed via shareware and mail order. The Ultimate Doom, an updated release of the original game featuring a fourth episode, was released in 1995 and sold at retail.
Doom was highly influential in the development of Duke Nukem 3D. In the 20th Anniversary Edition developer commentary, the Duke Nukem 3D developers repeatedly make reference to Doom. They explain that many of the features in Duke Nukem 3D were added to the game simply because 3D Realms felt they were in competition with id Software. If a feature existed in Doom, then the developers felt it needed to exist in Duke Nukem, and if a feature did not exist in Doom, then the developers were especially eager to implement it in Duke Nukem.