See Dennis Overbye's obituary...John Archibald Wheeler was born to a family of librarians in Jacksonville, Florida, in 1911. (Only my mother has been a librarian.) At the age of 21+, he received a PhD from John Hopkins University. His thesis was about helium.
Except for an interruption at University of Texas in Austin, he spent most of his career at Princeton University. The list of his famous PhD students is impressive. It includes Richard Feynman who needs no additional comments, Jacob Bekenstein of the black hole entropy fame, Charles Misner of their GR textbook fame, another co-author, cosmologist Kip Thorne, axiomatic field theorist Arthur Wightman, forefather of decoherence Hugh Everett (the term "many worlds" is due to Wheeler, of course), Bill Unruh, the father of the particle production in accelerating frames, and top skeptical climatologist Fred Singer. Wheeler was a great and caring teacher.
And he has changed the life of Daniel Holz of Cosmic Variance, too. Dan was apparently lucky to spend quite some time with Wheeler.
Wheeler's and Feynman's infantile but immensely playful attempts to regulate the divergent electromagnetic energy of a point-like electron have led Feynman to his correct (Feynman) propagator for the electromagnetic field. John Wheeler was the first person who defined the term S-matrix back in 1937. Nowadays, we think of the S-matrix as the conglomerate of nearly all physically meaningful information about a theory in particle physics, especially in the context of quantum gravity that doesn't admit local Green's functions.
Together with Niels Bohr and Enrico Fermi, John Wheeler is the father of nuclear fission. Even though Wheeler's original plan at Princeton was to talk to Einstein and debunk his opinions about quantum theory, Wheeler eventually talked to Bohr (in Copenhagen where he sailed) much more intensely: according to Wheeler, Bohr was on par with Jesus Christ et al. His and Bohr's liquid drop model of nuclear fission was born in 1939. His work on the Manhattan project was important and visionary. He was able to predict that by-products such as Xenon 135 would stop the reaction. After the Manhattan project, he continued with the Matterhorn B (fusion) project, leading to the H-bomb after some twists and turns.
Wheeler supported not only these bombs but also the Vietnam War and the missile defense system.
Once he was satisfied with his results in applied physics, he focused on general relativity. Between the 1950s and 1970s, he was attempting to realize Einstein's dreams and to find a unified field theory (of gravity and electromagnetism and maybe more) under Wheeler's own trademark, geometrodynamics. Much like Einstein's Ansätze, Wheeler's attempts didn't have much chance. For example, his framework couldn't account for fermions.
His inventions (or discoveries) in pure general relativity were more successful. In the early 1950s, general relativity was not even an acceptable field to teach at universities. Wheeler helped to change the situation profoundly. In 1957, he introduced and gave a name to wormholes. Even more importantly, ten years later, he coined the term black hole. At that time it became clear to him - partly because of Oppenheimer's precious comments from 1939 - that the gravitational collapse of a heavy enough star simply couldn't be stopped by any conceivable process and the resulting object whose geometry was known from the 1916 paper by Schwarzschild was bound to be important and needed a catchy name.
He invented the name "black hole" during a talk. You may try to guess where he gave that talk. Today, the place is also promoting catastrophic collapses of various cellestial bodies - albeit less realistic, less mathematically deep, less accurate, and less spectacular ones. Yes, it was at NASA's Goddard Institute of Space Studies (GISS). However, the talk took place well before James Hansen became the head of the institute to make sure that the real goal of the institute has no longer anything to do with space studies.
John Wheeler is also a co-father of the Wheeler-DeWitt equation, the vanishing Hamiltonian constraint applied to the "wave function of the Universe" in quantum gravity that is expected to replace the equations of motion as soon as it is properly formulated. The Hartle-Hawking wave function remains the most famous solution of the WDW equation. In quantum gravity, Wheeler also discovered and named one important mode of thinking about the Planckian physics, namely quantum foam.
In 1969, Margaret Mead, an anthropologist and a fan of sexual revolution, demanded that parapsychology would be included in AAAS (The American Association for the Advancement of Science). Ten years later, in 1979, John Wheeler thought that it was already the right time to explain everyone that parapsychology was a pseudoscience that should be eliminated from AAAS. He had to be in a minority because the Parapsychological Association remained an AAAS member.
John Wheeler liked to present everything about the Universe in terms of information - his it from bit became a rather popular cliché. He also liked to meditate about the anthropic principle, including its metaphysical versions whose scientific impact remains completely obscure to your humble correspondent, such as his "participatory anthropic principle" according to which the humans are participants in the process of bringing our past light cone into existence. ;-)
John Wheeler's most cited paper is actually his 1983 paper with Mandelbrot, The Fractal Geometry of Nature, with more than 11,000 citations.
At any rate, physics and the world are losing one of the last giants.