I believe he is a sorcerer. I don't think he has ascended to becoming a prince yet, but he appears to wield enormous powers, but they are limited to psychic abilities. He lacks physically as I believe the book mentions he is frail and needs support.
As to a God, I believe he is pledged to Nurgle. I don't think he would get the abilities he possess with the patronage of one of the Chaos Gods. As he is able to create plagues and disease I would assume that it's implied he has loyalty towards Nurgle