The events of Doom 1 and 2 happen, Doomguy gets frozen in Demoncarbonite, Eventually, Somewhere along the line Betruger finds out how to open the portal to Hell again, and the events of Doom 3 happen, the lone space marine of that eras UAC station on mars thinks he successfully stopped Betruger and the invasion, but he only stops it temporarily. Time passes, relative peace is had on mars and UAC covers up each of the incidents. Eventually, a rift on the surface of mars(called the fracture or something in this) opens, UAC and some brilliant scientist guy robot(?) build technology to harness the dimensional hell rift. This apparently solves the world power problem, and he somehow starts or somehow someone starts a fanatical cult and religion within the UAC at large. The events of DOOM 4 eventually transpire, as Doom guy is found in a tomb in hell, awoken and retrieves his armor to take the fight to the demons one more time.