Trivia: References to the game series include: Weapons: the BFG 9000, shotgun and chainsaw Characters: John Carmack (co-creator and former lead programmer of the series), Malcolm Betruger (Doom 3's antagonist) and the ship's AI Daisy (the name of protagonist Doomguy's pet rabbit) Enemies: zombified humans, the fireball hurling creatures (called imps in the game) Quotes: "I'm too young to die", "ultra nightmare" (the easiest and hardest difficulty settings respectively) Additionally, the name William J Blazkowicz is a reference to William Joseph "B. J." Blazkowicz, the protagonist of the Wolfenstein series starting with Wolfenstein 3D, the game that Id Software created prior to releasing the first Doom game.
Trivia: Spoilers: Among the video-tapes seen next to the TV after the opening credits are "C.H.U.D." and "The Goonies." This is quite relevant to the plot, in which it is revealed that the doppelgangers come from beneath the ground in a series of tunnels that used to be run by the government. "C.H.U.D." is about mutant creatures that live underground and have began to rise up and attack, like the doppelgangers, and "Goonies" takes place largely in underground tunnels and caverns, much like the film's climax.