I have wondered if I sequentially ask people who is the smartest living person they know, and ask that person next, would it lead me toward the same small group of geniuses. If I were doing that with the best living coder I might well start with Carmack. So next I'd have to go to Bellard, and hope that his answer isn't Carmack.
I can list a dozen or so co-workers from my time at Apple that I would choose in an instant.
There's a story along these lines about all the scientists / physicists involved in the Manhattan Project, ending with the answer being John von Neumann.