Henri Léon Lebesgue was born on June 28, 1875 in Beauvais, Oise, Picardie, France. He was educated at Ecole Normale Supérieure. Lebesgue was appointed as a professor at the Sorbonne in 1910.
Lebesgue's great contribution was the development of measure theory and the extension of the Reimann integral (named for Georg Riemann) to the notion of the integral of a function with respect to a measure. In addition, Lebesgue contributed to topology, Fourier analysis, and potential theory.
Lebesgue's major books include Leçons sur l'intégration et la recherché des fonctions primitives (Lessons on Integration and Research into Primitive Functions), published in 1904 and Leçons sur les séries trigonométriques (Lessons on Trigonometric Series), published in 1906.
Lebesgue died on July 26, 1941 in Paris.