[quote=@Lmpkio]
<Snipped quote by Spinosaurus>

No, I believe they are the same person. Doom Slayer is just what the demons call Doomguy back in the day, before they trapped him. He was then found by the UAC and so on.
[/quote]

But didn't the litch or whatever give him his armor while he was trapped in hell? That wouldn't make sense if it was his uniform in the first games.