Johnny Wheeler was one of the last surviving giants of physics from the earlier half of last century. Besides being a great physicist, he was also a great mentor, and a bridge between the generations of physicists. After his post-doctoral sting doing research with Niels Bohr, he advised an impressive list of students including mathematician Demetrios Christodoulou (who, together with my advisor, proved the nonlinear stability of Minkowski space; whose students include M. Dafermos and Gilbert Weinstein), Richard Feynman (nobel laureate for formulation of quantum electrodynamics, also known for his path integrals and diagrams), Robert Geroch (mathematical physicists focusing in general relativity and use of category theory in physics; mentor of Abhay Ashtekar), Charles Misner (coauthor with Thorne and Wheeler of "Gravitation", the M in ADM mass), Kip Thorne (great astrophysicist, perhaps best known for his bets with Hawking; a great teacher in his own right, advised Teukolsky and Price), Hugh Everett (many worlds interpretaion in quantum theorey), and Bill Unruh (having an effect named after you is usually a good sign of greatness; best known for his work in thermodynamics of black holes and quantum field theory on curved spacetime).

Some of Wheeler's most important contributions to physics include the formulation of the S matrix and geometrodynamics, as well as given les astres occlus their popular name: Black Holes. His career bridge quantum theory, general relativity, and post relativistic unified theories. As he puts it himself, he went through three phases in physics: before 1950 where "everything is particles", until recently when "everything is fields", and recently when "everything is information".

I only had the fortune of meeting him once. I was a freshman at Princeton, and Freeman Dyson was giving a talk. I remember that the talk was given in one of the third floor classrooms in Jadwin, which had 6 large rectangular tables in the room (a design that is rather awkward for a classroom). My friend Dan and I sat down at one of the tables (which turns out to be near the front; there were blackboards on three walls of the classroom and we couldn't tell which one was the "front" side). About 2 minutes after Dyson started talking, an old man slowly opened the door near the front and slowly walked in and sat couple of seats in front of me, to whom Dyson said "Hi, Johnny". I briefly talked to him (can't remember what we talked about) during the tea time that was after the talk. I remember truly shocked a couple days later when I found out that not only was he emeritus, that he still kept an office in Jadwin into which he comes at least twice per week.

John Archibald Wheeler, July 9, 1911 - April 13, 2008, of pneumonia.