Augustin-Louis Cauchy

Augustin-Louis Cauchy (Paris, August 21 1789 – Sceaux, May 23, 1857) was one of the most prominent mathematicians of the first half of the 19^th century. He gave a rigorous basis to the concept of limits. He established a convergence criterion for sequences of the type that are now called Cauchy sequences. The Cauchy condition for the convergence of series can be found in any present-day textbook on calculus. Probably Cauchy is most famous for his singlehanded development of complex function theory, with Cauchy's residue theorem as the fundamental result.

Reference

Bruno Belhoste, Augustin-Louis Cauchy: a biography, translated from the French by F. Ragland, Springer, New York (1991). ISBN 0-387-97220-X