My first thought when I heard, "wizard," was Merlin, although I did not like the casting of an African American as Lancelot du Lac any more than I would have liked a Caucasian as Mulan. It didn't make sense to me. I admit I never thought of Frankenstein because it just doesn't seem to fit. I also thought of Gandalf, but again, I would anticipate major licensing issues. I do like the idea of a scientist, but I'd have preferred someone like the Time Traveler from H.G. Wells', The Time Machine or Hari Seldon from Isaac Asimov's Foundation books.
I did not consider any of the Harry Potter wizards as a possibility because Rowling would have demanded a king's ransom for a license to use any of her characters even though one of them might have been a nice companion for Henry.