Russian mathematician Grigori Perelman, who was recently awarded the $1 million Clay Mathematics Institute Millennium Prize for solving the Poincaré conjecture in 2003, has turned down the money. Perelman felt that he didn't deserve the prize because he had merely built upon the work of US mathematician Richard Hamilton. Perelman, described by the Washington Post as "famously impoverished", is known for his eccentricities. Read more: Washington Post
All tortoises are actually turtles. Some turtles however are not tortoises.