Basically DOOM 1 was "Oh shit we're invaded" then everyone dies except you. Since you can't fly the shuttle back to Earth to save yourself, you decide to try to clear out the base. You kinda do, except you get ambushed and die. Because the base on Deimos is actually a part of hell now, that's where you "respawn" in hell. You clear out THAT base and its new commander and actually go to the outer levels of old school hell. Again, you clear THAT shit out, holy shit, and kill the guy leading the invasion on mars. The guy leading Hell basically gives you a teleporter to earth so that you'll stop messing shit up. That's right, HELL BROUGHT YOU BACK TO LIFE BECAUSE YOU KICKED IT'S ASS. Then you teleport to earth and OH SHIT DEMONS ARE HERE TOO! Apparently you meet the last few survivors and get them onto a space ship so they can get the fuck out of dodge. The problem is, the base where the launch button is? Overrun by demons. You clear THOSE demons out, launch the ship and save humanity. You're such a stone cold badass holy shit. Because you're tired as fuck, you decide to lie down and rest. Then some ****** commander says "So yeah, thanks and all. Oh yeah, we found out where they're coming from. Its your hometown." So you get the fuck back up. THEN you fight your way to your hometown and find where the demons are coming from. Do you go through the portal? Shit yeah you do, holy **** there are still demons to kill motherfucker. So you fight your way through the SERIOUS part of hell, then kill SATAN. Unless Plutonia/TnT are considered canon. Then its just some bigass guy that's like Satan's best friend, and you never kill Satan. And that is why the Doomguy is the single most powerful human in the history of all games everywhere. Even fucking jrpg ******s need a group of 3 people to kill God. By himself. Doomguy does it without magic or friends and kills Satan + whoever the fuck is close to Satan at the time.