CT idea/headcanon: Doomguy was the original template that all Astartes are based on and has since become a living pseudo-Primarch demigod of righteous fury, unstoppable wrath, & willpower who can even kill semi-divine god-like beings (reflecting his characterization in DOOM Eternal)
i’ve done a previous story exploring what Doomguy might be like in this AU (effectively a time-lost BJ from Wolfenstein having spent a LONG time fighting demons and only recently was rediscovered), but there’s plenty of room to have this here!
Like, push back BJ’s time to pre-cataclysm times, predating the Primarch’s creation so that he could have become this template, or whenever they would have been made. (For example, perhaps the Emperor created the Primarchs to protect humanity and those standing with them during the worse of the Cataclysm, in a more benign take of the Eternal Crusade from 40k canon, with the Primarch’s physical bodies being ideal vessels for their divine essence?)
Doomguy would be similar to a Thunder Warrior, though less obviously inhuman than an Astartes. Unless we just go whole hog and make him a post-human super soldier on par with regular Astartes, or even Custodians? that sounds kinda cool.
In this case, he was thought lost but then... fiends exploited loopholes in their non-aggression dealing with the divine forces (who may have helped place BJ in the right place to do as much damage as possible, as them acting directly will allow the fiends to harm mortals at will), and BJ plunged into the hell realms to fight them back and give people time to get away.
Now, a countless eternity in the hells, exposed to mutagenic energies, belief in him as the breaker of fiends and his own ravenous hatred has made him into something... else.
I’m liking the idea of him being a Primarch to the Custodes, specifically! At the very least, they were modeled after him even if they’re not QUITE the same thing. (He’s certainly a bit loopy enough to be one, between rambling about huge cuts and deploring the state of the environment while being menaced by zombies.)
