Doom (typeset as DOOM in official documents)[1] is a 1993 science fiction horror-themed first-person shooter (FPS) video game by id Software. It is considered one of the most significant and influential titles in the video game industry, for having ushered in the popularity of the first-person shooter genre. The original game was divided into three nine-level episodes and was 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.