He solved a century-old math problem, then refused both prizes for it
In 2002-2003, Russian mathematician Grigori Perelman posted three papers online proving the Poincare conjecture, unsolved since 1904. In 2006 he turned down the Fields Medal, math's highest honor, and in 2010 he declined the Clay Institute's $1 million Millennium Prize. He said his contribution was no greater than the mathematician whose earlier work he built on, then largely withdrew from mathematics.