Doom 64

You killed the Demons once, they were all dead. Or so you thought... A single Demon Entity escaped detection. Systematically it altered decaying, dead carnage back into grotesque living tissue. The Demons have returned - stronger and more vicious than ever before. You mission is clear, there are no options: kill or be killed!

In the aftermath of the lone Marine's legendary victories against the forces of Hell, the ravaged research installations of the Union Aerospace Corporation are sealed off under quarantine, left to fester beneath apocalyptic levels of radiation. For years the abandoned facilities lie silent.