Augustin-Louis Cauchy

Trained as a civil engineer at the École des Ponts et Chaussées, Cauchy worked on military fortifications at Cherbourg before turning entirely to pure mathematics on the encouragement of Laplace and Lagrange. In his 1821 Sorbonne textbook Cours d'Analyse, he transformed calculus by replacing imprecise infinitesimals with precise limit definitions.

He single-handedly created the theory of complex functions with his 1825 memoir on contour integrals, formulating Cauchy's Integral Theorem, Cauchy's Residue Theorem, and the Cauchy-Schwarz inequality. A devout legitimist Catholic, he accepted exile in Prague rather than take the constitutional oath to King Louis-Philippe.