Tridgell is possibly the most intelligent person I've ever met, and I've met Torvalds and a bunch of other Linux developers -- not that they aren't intelligent too, among them might be a challenger to that title.

Tridge has a way of explaining complicated ideas in a way that pares them down to their essence and helps you to understand them that just really struck me (a smart person is able to talk about a complicated thing in a way that makes you feel dumb, a really smart person is able to talk about a complicated thing in a way that makes you feel like a genius). As well as the ability and intellectual curiosity to jump seemingly effortlessly across disciplines.

And he's a fantastic and very entertaining public speaker. Highly recommend any talk he gives.