I'm pretty sure he's one of the smartest people in history in terms of raw intellect. My favorite story about him is when George Dantzig (the guy who accidentally solved two famous unsolved problems in statistics, thinking they were homework) once brought John von Neumann an unsolved problem in linear programming, on which there had been no published research, saying it "as I would to an ordinary mortal." He was astonished when von Neumann said, "Oh, that!" and then proceeded to give an offhand lecture lasting over an hour, explaining how to solve the problem using the then unconceived theory of duality.
