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.
Cyberdemon
In the action role-playing game "Doom RPG", the Cyberdemon is created by an occultist scientist Kronos. In "Wolfenstein RPG", the Cyberdemon appears as the Harbinger of Doom, summoned by the Nazis at Castle Wolfenstein during World War II. American commando William "B.J." Blazkowicz defeats it using the Spear of Destiny, destroying its right leg and left arm, and the Harbinger vows that it would have a rematch with Blazkowicz's descendent in the future, which happens when Stan Blazkowicz faces it in "Doom II RPG".