Grigori Yakovlevich Perelman (1966-, sometimes seen as Grisha Perelman) is a Russian mathematician who has made great contributions to Riemannian geometry and geometric topology. He also is credited with solving the Poincaré conjecture, a topological problem posed in 1904; he may have also proven Thurston’s geometrization conjecture. Some sources say he no longer practices mathematics. He has been offered several mathematical awards in the past, which he turned down; one was the Clay Millennium Prize for the resolution of the Poincaré conjecture, but he cited American Richard Hamilton’s contribution, a mathematician who suggested a program for the conjecture’s solution.