The Russian mathematician Grigori Perelman did not accept the Fields Medal in 2006 and refused the million dollar prize for solving Poincaré's conjecture, one of the millennium problems, in 2010.

The Poincaré conjecture is a topological problem established in 1904 by the French mathematician Henri Poincaré. It characterises three-dimensional spheres in a very simple way. This problem was directly solved between 2002 and 2003 by Grigori Perelman, and as a consequence of his demonstration of the Thurston geometrisation conjecture.