Today is the 100th birthday of Jean-Pierre Serre, the last of the twentieth-century mathematical titans. His most recent paper is less than a year old. By all accounts, he is still actively doing research.

When Serre was awarded the Fields Medal in 1954 at the age of 27, he was introduced to the audience by Hermann Weyl a titan of an earlier age. “Never before”, said Weyl, “have I witnessed such a brilliant ascension of a star in the mathematical sky”.

It’s been pointed out that Serre now holds the distinction of being both the youngest and the oldest Fields medalist ever.

Unlike most of the other great mathematicians of his era, Serre worked in, and left a lasting imprint on, and in some cases completely transformed an astonishing variety of different mathematical subfields. His collaborations, often uncredited, are legendary. He was arguably the one collaborator who was absolutely necessary to Grothendieck. The proof of Fermat’s Last Theorem relies on a key observation of Serre’s (though in this case I’m guessing — but not certain — that while Serre sped things along, he doesn’t count as indispensable). Wikipedia lists over 30 “things named after Jean-Pierre Serre”. The list is incomplete (Where is “Serre’s GAGA”? Where is Auslander-Buchsbaum-Serre? Where are Serre’s regularity conditions?) but it still includes quite a few items that most mathematicians would be proud of as a once-in-a-lifetime accomplishment.

Once when I was very young (younger even than the age at which Serre won his Fields medal), I got up my courage and asked a senior mathematician a question that I was sure was extremely naive and silly but that I just couldn’t seem to figure out on my own. He was a very good senior mathematician, but his judgment was clearly quite imperfect, because he insisted that I send my question to Serre via an ancient system of communication that we called “airmail”. I balked, but the senior mathematician browbeat me into it. Two weeks later (which is about as soon as was physically possible in those days) I got back a three-page handwritten letter from Serre, making it crystal clear that the question was exactly as naive and silly as I thought it was, but taking the opportunity to teach me some related mathematics. It was kind, generous, and surely an extremely poor use of his time. I wonder what great theorem the world has been denied because I failed to stand by my “let’s not bother him” instinct.

But French mathematicians as a group are well known for their occasional sharp tongues. Here’s a story I’ve been told, which might or might not be entirely apocryphal. Serre once attended a lecture by another prominent mathematician, who, by some accounts, Serre considered both overrated and arrogant. That other mathematician (who I won’t name partly because this whole story might be fiction) started out by writing several theorems on the blackboard and then announcing that although the theorems were all pretty good in their own right, the best thing about these theorems was that they all followed from just one idea. At which point Serre raised his hand and corrected the speaker: “At most one idea.”

Again, I don’t know whether that one’s true. I do know that almost all of the mathematics that I know and love bears Serre’s imprint. I wish him a very happy birthday, and many more.