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.
Strife (1996 video game)
After the game's official support ended, game engine recreations of "Strife" were created by Doom source port developers through reverse engineering. Notably authors were Jānis Legzdiņš (author of the Doom source port Vavoom), Randy Heit (author of ZDoom), Samuel Villarreal (author of "SvStrife"), and James Haley (author with Samuel Villareal of Chocolate Strife). Except for the last, these allow for high resolution graphics modes, better mouselook, and expanded modding capabilities.