Doom 64

Following the Doom Marine's success at thwarting Hell in Doom, Doom II: Hell on Earth, and in the Final Doom storyline, a quarantine is established on the U.A.C. research installations with apocalyptic levels of radiation. For years, the installations stood abandoned, until a barely-functioning satellite monitoring one of them sends a message back to Earth. This message indicates that a "single entity with vast rejuvenation powers" was masked by the radiation and escaped detection. The entity was able to resurrect the demons by altering "decaying dead carnage back into corrupted living tissue". As the only experienced survivor of the Doom episodes, the Marine is sent in alone to exterminate them.
However, the Marine realizes the demons have planned to lure him back into Hell. They are nonetheless unable to defeat him, and with the Unmaker, he eventually battles and kills the Mother Demon. The game ends with the Marine, no longer capable of having a normal life following his encounters with Hell's forces, deciding to remain in Hell forever to ensure no demon ever rises again.
In the Lost Levels from the 2020 remaster, the story continues as the Mother Demon was revealed to have a sister called the "Resurrector". It banishes the Marine back to a UAC base, forcing him to fight his way back to Hell to stop the Demons. It branches the storyline between the original games with the 2016 reboot of Doom and Doom Eternal.