The only guess that other readers have offered was Michael Boris Green, a prominent figure of the first superstring revolution and a great superstring & supergravity expert. Ladies and Gentlemen, there were not too many excellent choices but this one became a reality. Congratulations.
Had I known that this physicists' chair was actually a mathematics chair, I would have told you that Michael Green was the only solution.
The chair was created in 1664. Green's predecessors include Isaac Newton, Charles Babbage, Paul Dirac, and Stephen Hawking. See:
TRF: 25 years of the first superstring revolutionThe first superstring revolution was approximately as important for the progress in theoretical physics as Hawking's semiclassical calculations of the black hole evaporation. It just came one decade later.
TRF: The next revolution
TRF: Green's Strings 2008 talk
TRF: Non-decoupling of N=4 d=4 SUGRA
TRF: Finiteness of supergravity theories
TRF: A curious truncation
TRF: N=8 SUGRA & Lance Dixon's puzzle
TRF: Two roads from N=8 SUGRA to strings
TRF: 275 more texts with "Michael Green"
MBG's papers: SPIRES
MBG's papers: Google Scholar
News: Physics World
News: The Guardian
News: The Times
News: The Telegraph
News: Cambridge Evening News
News: Business Weekly
Much like Stephen Hawking had another great physicist by his side who was necessary for his major achievements - Jacob Bekenstein - Michael Green had one, too. A difference is that both Green and Schwarz were genuine masters of the technology (and there were other people who have quickly contributed a lot) while Jacob Bekenstein has always been a kind of prophet.
Green is also a co-author of the first major textbook on superstring theory. A badly inaccurate yet funny joke says that in the Green-Schwarz-Witten book, the cover is green, the writing is schwarz (black), and it's written by Witten. ;-)
For reasons that are partially understandable and partially nontrivial, Michael Green remains more active than Stephen Hawking. At any rate, I hope he will enjoy the chair that naturally belongs to him.