Lebesgue, Henri Léon (1875–1941)

French mathematician who developed a new theory of integration, now named after him. He also made contributions to set theory, the calculus of variations, and function theory.

Lebesgue was born in Beauvais and educated at the Ecole Normale Supérieure in Paris. He was professor at the University of Poitiers 1906–10, when he was appointed lecturer in mathematics at the Sorbonne. In 1920 he was promoted to the chair of the application of geometry to analysis, but he left the Sorbonne 1921 to take up his final academic post as professor of mathematics at the Collège de France.

Lebesgue was intrigued by problems associated with Riemannian integration. His introduction of the Lebesgue integral quickly proved to be of great importance in the development of several branches of mathematics, especially calculus, curve rectification, and the theory of trigonometric series.

Following the work of Emile Borel, Lebesgue laid the foundations of the modern theory of the functions of a real variable.