Widely considered the preeminent French mathematician of the 20th century, Jacques Hadamard has made an impact on many fields of mathematics. Although an analyst and a student of theoretical calculus by training, he has influenced topology, number theory, and even psychology. His work on defining functions won him the Grand Prix of the Académie des Sciences early in his career, and his proof of the prime number theorem solidified his importance in the mathematical world. He wrote several textbooks on a variety of mathematical subjects, including one which explained a mathematician's thought processes. Hadamard was first and foremost a teacher, however, and he used his position to help both students and colleagues alike see the connections between seemingly unrelated fields.

Born in Versailles on December 8, 1865, Jacques-Salomon Hadamard was the son of two teachers. His mother, Claude-Marie Picard, taught piano, while his father, Amédé...