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.
John Romero
Romero worked at id Software from its inception in 1991 until 1996. He was involved in the creation of several milestone games, including "Commander Keen", "Wolfenstein 3D", "Doom", "" and "Quake". He served as executive producer (and game designer) on "Heretic" and "". He designed most of the first episode of "Doom", a fourth of the levels in "Quake", and half the levels in the "Commander Keen" and "Wolfenstein 3D: Spear of Destiny". He wrote many of the tools used at id Software to create their games, including DoomEd (level editor), QuakeEd (level editor), DM (for deathmatch launching), DWANGO client (to connect the game to DWANGO's servers), TED5 (level editor for the "Commander Keen" series, "Wolfenstein 3D: Spear of Destiny"), IGRAB (for grabbing assets and putting them in WAD files), the installers for all the games up to and including "Quake", the SETUP program used to configure the games, and several others. In his keynote speech at WeAreDevelopers Conference 2017, Romero named this period Turbo Mode, in which he emphasizes having created 28 games, in 5.5 years with a team consisting of fewer than 10 developers.