In 2002, the Russian mathematician Grigori Perelman solved one of the most fascinating mathematics problems of our time; The Poincare Conjecture: a hypothesis, which is now a theorem, that states (very roughly) that anything that locally looks enough like a three sphere must actually be a three sphere. Originally posed in 1904 by Henri Poincare, Perelman proved the result in 2002. Due to its beautiful simplicity in statement and extreme difficulty in establishment, this problem was one of those on the list of Millennium Prize Problems. Successfully solving one of the problems highlighted on this list earns the work a $1000000 prize. Nice reward for nice work, no?
It turns out that Dr. Perelman is not one for fanfare, or notoriety. He has been nicknamed "Mathsputin" due to his efforts to live simply and remotely. In character with these efforts, he has refused the gift.
Beautiful mathematics is its own reward. I get that.
But perhaps one should take the money and donate it?