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.
Id Tech 4
id Tech 4, popularly known as the "Doom 3" engine, is a game engine developed by id Software and first used in the video game "Doom 3". The engine was designed by John Carmack. Carmack also created previous game engines, such as those for "Doom" and "Quake", which are widely recognized as significant advances in the field. This OpenGL-based game engine has also been used in "Quake 4", "Prey", "", "Wolfenstein", and "Brink".