Jascha Hoffman in the New York Times Book Review:
In 1904 the French mathematician Henri Poincaré made a conjecture about three-dimensional space that may help to explain the shape of the universe. Although it was crucial to the growth of the field of topology, Poincaré’s conjecture resisted proof for a century. When a Boston philanthropist announced a million-dollar prize for its solution in 2000 it was unclear whether he would ever have to pay.
Then, in 2002, a Russian mathematician named Grigori Perelman posted a terse paper to an online archive. In the course of tackling a broader problem, Perelman seemed to have miraculously swept away the remaining obstacles to proving the Poincaré conjecture. Soon the mathematical rumor mill was buzzing. The proof seemed genuine, but word was that Perelman had no plans to publish it.
This was only the beginning of the weirdness.