"Smart" isn't a single dimension, and at some level I lose the ability to evaluate: you might be a brilliant genius linguist, but how would I evaluate that?

In the realm of coding I would definitely put Andrew Tridgell (Samba, rsync etc) and Linus Torvalds (Linux, git, etc) up there as some of the smartest people I've worked with, and hands down Andrew Tridgell was the nicest to work with.

But I don't really think like that, I use a simple yardstick: are they smarter than me? If so, and they're nice, I want to work with them! In the lightning world, there's no doubt in my mind that Lisa Neigut, Bastien Teinturier and Olaoluwa Osuntokun are smarter than me, for example: my ego simply serves to make me strive to keep up!