Pierre de Fermat was a French mathematician born near Montauban in 1601, and died at Castres on January 12, 1665. He is often called the founder of the modern theory of numbers. He did this incidentally to his preparation of an edition of Diophantus, and the notes and comments thereon contained the numerous theorems of considerable elegance necessary to develop the theory of numbers.
Together with Rene Descartes, Fermat was one of the two leading mathematicians of the first half of the 17th century. Independently of Descartes, he discovered the fundamental principle of analytic geometry. His methods for finding tangents to curves and their maximum and minimum points led him to be regarded as the inventor of the differential calculus. Through his correspondence with Blaise Pascal, he was a co-founder of the theory of probability.