Eternal Darkness: Sanity's Requiem is an action-adventure video game developed by Silicon Knights and published by Nintendo. Originally planned for the Nintendo 64, it was switched to the GameCube for development and released on June 24, 2002. While the game features similar gameplay mechanics to that of Resident Evil, it distinguishes itself with unique features, such as "sanity effects". In the game, players take on the role of several characters as they battle a powerful entity who seeks to enslave humanity.

When Silicon Knights began work on Eternal Darkness, their intention was to create a game "that was in the horror genre, but not categorized as survival/horror",[3] with then later labeling it as a "psychological thriller" during an early interview with IGN, as opposed to, what they referred to as, the "B-movie horror plots" of Resident Evil.[4] At the same time, Denis Dyack remarked during an interview about his decision to design the game with the intention of "messing with people's heads", after being inspired by media reports.[3]  The game was initially planned for the Nintendo 64 and to feature several characters, including "a Special Forces commando deep behind enemy lines", with the developers showing off the early builds during the 1999 E3 Expo;[5] Silicon Knights later changed their mind and rebuilt the game in order to make it a launch title for the Nintendo GameCube. It never made it as a launch title, as development was delayed.[6]