Here is the obituary of the great geometer/topologist. In grad school I studied topology a bit and got to the point where I could more or less understand some of his work. It was one of the many cases in which I was struck by the utter beauty of mathematics.
But on occasions like this, I find I am inevitably sad in a way that goes beyond the loss of a magnificent mind. Virtually no one in the US will have had a clue who this person was. Does that matter? It isn't like it is important for everyone in society to know anything about topology, certainly not enough to understand why he was a genius. But what is important - indeed, in my view, what is essential for the continuation of civilization beyond the next 100 years - is an educated, critical, intellectually and politically engaged populous. And if we were to take serious steps to try to bring that about, it would involve radical changes to our education system, our entertainment system, our press, our economy, etc. And any plausible institutionalization of a serious inclination to create an educated, critical, and engaged populous, I suspect, would generate as a side effect a rock star status for someone like William Thurston.
So when I read the New York Times - which was surely one of the few outlets to even notice - and see more prominent coverage of the fact that Prince Harry took his clothes off than I do of this loss, I take it to be a very bad sign indeed for the future of humanity.