>>529963226
depends on when you ask. it used to be he was the forced reincarnation of a whole bunch of shaman psyker types who were dying and not coming, mass suicided to take on whatever it was that was eating them and out shits the emperor.

currently: he was a powerful psyker(stupid powerful but JUST a powerful psyker.) then somewhere along the way, made a deal or some sort of pact with the chaos gods - turned up, stole the power he was bargaining for and fucked off without honouring his part I guess and sometime between before, then and now became in opposition to them in a literal sense, his warp juice is anethema to them - which is why they call him that. -

as for the pre-Emperor business. He was just a very long lived dude who saw the rise and fall of it all, then in the era of the techno barbaric earth he rose to power using extensive and powerful biomancy and gene augmentation to make thunder warriors: proto-spacemarines who threw all care to the wind about long term survival and reasonable power and made a bunch of cavemen with radiation guns and set about subjecting to the earth to his will.

then he killed all those guys, installed the Custodes and set to work on the Primach project and the Astartes (space marines.) projects.

is Rogue Trader worth it? I didn't get through wrath of the righteous due to the abyss / hell levels being a fucking slog and the map mechanic being just awkward to deal with.