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.
Doom (1993 video game)
In addition to the main single-player game mode, "Doom" features two multiplayer modes playable over a local network: "cooperative", in which two to four players team up to play through the main game, and "deathmatch", in which two to four players play against each other. Online multiplayer was later made available a year after launch through the DWANGO service. "Doom" also contains cheat codes that allow the player to be invulnerable, obtain every weapon, be able to instantly kill every monster in a particular level, and several other abilities.