Doom (1993 video game)
The ability for others to create custom levels and otherwise modify the game using WAD files turned out to be a popular aspect of "Doom". Gaining the first large mod-making community, "Doom" affected the culture surrounding first-person shooters, and also the industry. Several future professional game designers started their careers making "Doom" WADs as a hobby, among them Tim Willits, who later became the lead designer at id Software.
Doom engine
id Tech 1, also known as "Doom" engine, is the game engine that powers the id Software games "Doom" and "". It is also used in "Heretic", "", "Strife: Quest for the Sigil", "Hacx: Twitch 'n Kill", "Freedoom", and other games produced by licensees. It was created by John Carmack, with auxiliary functions written by Mike Abrash, John Romero, Dave Taylor, and Paul Radek. Originally developed on NeXT computers, it was ported to DOS for "Doom"'s initial release and was later ported to several game consoles and operating systems.