Actually, it was made specifically for Doomguy by a demon known as The Wretch, who was the reborn, corrupted soul of the son of one of the Night Sentinels. That's how the Demons managed to destroy Argent D'Nur. They made a deal with the betrayer that he gets his son back if he lets the demons in. The demons, surprising abso-fucking-lutely no one, corrupt his soul and made him a demon, give him to retard daddy, and presumably rip him and the rest of Argent D'Nur apart, shitting and giggling as they went.
Some unspecified time passes as Doomguy makes Hell figuratively and so very literally shit themselves by killing everything he sees, and Wretch and Doomguy meet up once more.
Wretch is like,>Hey, you want some armor that heals you, repairs itself, and makes you ammo for your favorite gun by literally drinking the blood of demons?
And Doomguy is like,>Bitch, you get to live.
And that's how he got the Preator suit.