V. H. Satheeshkumar has brought my attention to an 8-page document
Adventures in physics and math (a commemorative popular lecture)in Witten's folder of a server at Princeton's IAS. It's a lecture Edward Witten gave somewhere in Japan – but I don't know when he gave it.
Those 8 pages are large and dense – maybe designed to save the paper and forests. (When I was printing lectures, I surely liked to save the paper – and time of printing – as well. An example.) I recommend you to read it because the talk is very interesting. Below, you may find just some sketches of the information from the talk.
While everyone knows that Edward Witten has worked for the McGovern presidential campaign in order to build a Big McGovernment, the talk focuses on science only.
As a kid, he wanted to be an astronomer. It is easier for him today to find Saturn in kids' telescopes than it was when he was a boy. He believed that all astronomers would have to become astronauts by the time he would grow up. His parents didn't want to push him to mathematics or sciences so he was only exposed to uninspiring standard level mathematics and theoretical physics for quite some time.
Around age 21, he was decided to become a theoretical physicist. The excitement in particle physics and an apolitical November revolution have played a role. Theoretical physics is better than mathematics for some reasons (I agree with all these claims and their justifications, much like pretty much all other opinions in the essay).
While at Harvard, Witten was strongly affected by Sidney Coleman (and his interest in strong coupling was important later), shared an office with Howard Georgi, and Sheldon Glashow was a senior physicist over there. Ed married a student of Arthur Jaffe. (All those things must be as interesting to read as they are for me for everyone who has spent at least 5 years in the Greater Boston physics environment.)
Witten has had a split personality for 2 decades, working on some tangible particle-physics-phenomenological quantum field theory; or on mathematical-or-topological aspects of quantum field theory. The relationships between these two parts of the field became a bit more clearer in the 1990s. His interest in the Green-Schwarz 1984 paper helped to kickstart the First Superstring Revolution. But in the talk, you may learn that he wasn't an immediate convert who has learned everything he needed in days. Instead, he was heavily interested in the papers on superstrings around 1982, and spent lots of time with them.
(This was obviously true when I was entering the field as well. I think that it's much more general. Think about Einstein's teenage dreams in which he was chasing girls moving by the speed of light. Can he catch them? People generally play with highly related ideas years before everyone may see that they're doing something important with them. People are getting ready for a revolution in several previous silent years.)
Witten's most productive years were 1994-1995, in the Second Superstring Revolution (M-theory is discussed there a bit), and I believe that many others would order his contributions in this way, too. I surely would. You may learn some basics of string theory and why it's almost certainly a move in the right and deeper direction; as well as some aspects of his research into knots, strongly coupled supersymmetric theories, and many other things.