Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150807010020/@comment-14745711-20150807070357

The Emperor has always had his powers, since he is the incarnation of thousands of early Neolithic human shamans, who all committed suicide in order to create a man who would be able to protect humanity from the dangers of the Warp. Admittedly it take a while for his powers to fully manifest, but it did not require any help from the chaos gods, so no, as far as the current cannon is concerned there was no bargain with the dark gods. 40k is full of various contradicting threads of information, and this sounds like one of them. Since it is not the origin story for the Emperor held by most people at the current time, then it doesn't count as true cannon.