Corypheus is a darkspawn and a former magister with red lyrium in his flesh. He was one of the magistrates who entered the fade physically and saw the throne of the gods. Contrary to what the chantry claims, Corypheus says when he got there it was already tainted and empty. There was no voice of the Maker, only empty whispers.
He is well acquainted with the elven trickster god, Fen Haral - the dread wolf, and was given an orb that contained the trickster gods power. There seems to have been some sort of an agreement or deal between the two with regards to unlocking its power since the dread wolf was too weak after a long slumber. Corypheus turned on the wolf and attempted to alter the orb to act as a means to once more enter the fade physically and attempt to become a god.