Board Thread:Warhammer 40k General Discussion/@comment-7289991-20130504045808/@comment-5574937-20130514184006

To put it simpily the emperor is not malice he is the rencarination of all the shamans that used to guide humanity  but because when they died they were beign picked off one by one when they died by deamons the gathered together and commited sucide and all their souls got reborn as the emperor.

So how the emporor came to be is pretty well explained and the reason he is so powerful is because he was orginally a few thousand psykers.

look here