French lawyer who pursued mathematics in his spare time. Although he pursued mathematics as an amateur, his work in number theory was of such exceptional quality and erudition that he is generally regarded as one of the greatest mathematicians of all times. He had the habit of scribbling notes in the margins of books or in letters to friends rather than publishing them. He discovered analytic geometry independently of Descartes, but did not publish his work. He founded the theory of probability with Pascal and discovered the least time principle which states that light will travel through an optical system in such a way as to pass from starting to ending point in the least amount of time (a concept from calculus of variations ). Fermat solved many fundamental calculus problems, and made important contributions to number theory and optics. He was also fluent in French, Italian, Spanish, Latin, and Greek.

He is most famous for scribbling a note in the margin of a book by Diophantus that he had discovered a proof that the equation xⁿ+yⁿ = zⁿ has no integer solutions for n>2. He stated "I have discovered a truly marvelous proof of this, which however the margin is not large enough to contain." The proposition, which came to be known as Fermat's last theorem, baffled all attempts to prove it until A. Wiles succeeded in 1995.

Descartes, Diophantus, Pascal

Additional biographies: MacTutor (St. Andrews), Dublin Trinity College