A leading mathematician of the 17th century. In number theory he proved Fermat’s Little Theorem and Fermat’s Two Squares Theorem and famously conjectured Fermat’s Last Theorem. He independently introduced Cartesian coordinates, and his work on tangents was an acknowledged inspiration to Newton in the development of calculus. In a correspondence of 1654 with Pascal, they laid down the foundations of probability. Professionally he was a lawyer in Toulouse, and so he was considered the ‘Prince of Amateurs’.