Himself. No other way he could do the things he does, there being too many of them and too varied.
Poked for a minute about my memory of fairy tales with sorcerer kings. There's the one in "Penta of the Chopped-off Hands," for instance.
Whereupon I remember all the shape-shifting wizard's apprentices who married a princess after outwitting their masters. That would be a sorcerer king. . . except the king's particular brand of conceit would not mix well with such a story, and his relationship with his wife wouldn't fit what the story says it is.
So, they just had an arranged marriage, a la "Goose Girl" without the added drama, and he just studied magic. Now all I have to establish is that he wasn't so conceited that he wouldn't have bothered to study it. . . probably it was acquiring them that made him so.