George Daniel Mostow (born July 4, 1923) is an American mathematician, renowned for his contributions to Lie theory. He is the Henry Ford II (emeritus) Professor of Mathematics at Yale University, a member of the National Academy of Sciences, the 49th President of the American Mathematical Society (1987–1988), and former Trustee of the Institute for Advanced Study in Princeton, NJThe rigidity phenomenon for lattices in Lie groups he discovered and explored is known as Mostow rigidity.