A (very) Brief History of Henri Lebesgue

Henri Léon Lebesgue (June 28, 1875 – July 26, 1941) was a French mathematician known for his theory of integration, which was a generalization of the 17th-century concept of integration—summing the area between an axis and the curve of a function defined for that axis. 

Lebesgue's first paper was published in 1898 and was titled "Sur l'approximation des fonctions". It dealt with Weierstrass’s theorem on approximation to continuous functions by polynomials. 

Between March 1899 and April 1901 Lebesgue published six notes in Comptes Rendus. The first of these, unrelated to his development of Lebesgue integration, dealt with the extension of Baire's theorem to functions of two variables. 

The next five dealt with surfaces applicable to a plane, the area of skew polygons, surface integrals of the minimum area with a given bound, and the final note gave the definition of Lebesgue integration for some function f(x).