He is particularly famous for his ‘last theorem’, which he discovered in about 1637, and of which he claimed he had a ‘marvellous demonstration’. He died without revealing his proof and it was not until 1994 that the English mathematician Andrew Wiles gave a full proof. The son of a wealthy leather merchant, Fermat was educated at a Franciscan monastery and studied law at U Toulouse. He became a judge, but he had a passion for mathematics and obtained many mathematical theorems, which he communicated to fellow mathematicians, always remaining very secretive about his proofs. The correspondence between Fermat and Pascal laid the foundations of the modern theory of probability. A lunar crater and a street in Paris are named after him.

http://scienceworld.wolfram.com/biography/Fermat.html Fuller biography and portrait.