SPOILER: so whats the deal with Doom Guy in this installment?

SPOILER: I just finished the campaign (This game was amazing) and I'm still trying to figure out exactly what Doom guy is in this installment. From all of the artifacts that tell a story it almost seems like the original games took place before this but I know that this is supposed to be a reboot. Either that or the Doom guy isn't human in this one and he's some type of pre-human race that fought against hell in the past. Thoughts?