Robert E. Kottwitz

William J. Friedman and Alicia Townsend Friedman Professor. Works in the region where algebraic geometry and automorphic forms meet. Gave a proof of a longstanding conjecture by A. Weil on Tamagawa numbers of semisimple groups. Proved a conjecture of Langlands on the reduction of certain Shimura varieties modulo a prime p. The result opened the way to proving reciprocity laws between the arithmetic data of these algebraic varieties and the analytic data obtained from the spectral theory of automorphic forms. Later work is related to the proof of the fundamental lemma-a central result in p-adic harmonic analysis.