I remember that a philosophy professor called John von Neumann the smartest person who has ever lived. Do you think so too?

Yes! Though it depends a bit on what you he meant by 'smart'. In terms of the sheer firepower of his brain, I don't think we know of anyone who was a faster mathematical thinker than von Neumann. His friend, Wigner, claimed that while JVN had the most exceptional brain among any of the incredible geniuses they both knew, Einstein was the the deeper thinker. People thought von Neumann was less of a creative thinker--he tended to bulldoze his way through problems. But I think that was a little unfair on him. I think it's only really now, more than half a century on, we're really beginning to appreciate how prescient his contributions really were.

I focused on his contributions to mathematical logic and the foundational crisis in maths (because that ends up being key to his thinking later), then the science, engineering and maths that is most relevant to us today. So there's a huge swathe of his mathematical contributions I almost completely ignore. There's a whole branch of algebra (https://en.wikipedia.org/wiki/Von_Neumann_algebra) he invented that gets a cursory mention in the book. But Vaughan Jones won the Fields Medal as a result of exploring just a small part of it!