Robert Graham Leigh is a Canadian physicist working on string theory.

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Leigh obtained his B.Sc. degree from the University of Guelph in 1986, and his Ph.D. from the University of Texas at Austin in 1991, working with Joe Polchinski. After postdoctoral positions at Santa Cruz and Rutgers, he has been a professor at the University of Illinois at Urbana-Champaign since 1996. Since 2007, he has been a Fellow of the American Physical Society.^[1]

Leigh discovered, in association with Dai and Polchinski, an important class of extended objects in string theory, the D-branes.