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.
Duke Nukem (character)
Duke Nukem was initially created in 1987 by chief programmer Todd Replogle of Apogee Software (now 3D Realms) as the protagonist for the video game he was designing titled "Metal Future," which was set in the then-near future of "one decade later from now" in 1997. After hearing the character's name, producer and founder of Apogee, Scott Miller, suggested the game should have the same name, and he helped design the character. Artwork was produced by George Broussard, Allen H. Blum III, and Jim Norwood. Duke was not voiced, but spoke through on-screen text.