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.
Iikka Keränen
In his teens, Keränen programmed freeware games for the Commodore Amiga. Later he created the popular "Quake" mod "Airquake", as well as over a hundred free add-on levels for the "Doom" and "Quake" series of first-person shooters. He was named the top "Doom" level maker of all time by Doomworld in 1998, described as "one of a few pioneer level designers that created the new bottom line for playability and design in "Doom" levels, as well as helping to develop some of the special FX that many level authors now take for granted".