Augustin-Louis Cauchy

Cauchy is most famous for introducing rigorous definitions and proofs into calculus, including the modern epsilon-delta definition of a limit and the formal definition of continuity. His textbooks Cours d'Analyse, published in 1821, set new standards for mathematical rigor and became foundational references in real analysis.

Cauchy was one of the most prolific mathematicians in history, publishing over 800 papers and several books across his career. His collected works, Oeuvres complètes d'Augustin Cauchy, span 27 volumes and were still being compiled decades after his death in 1857.

Cauchy developed the core results of complex analysis, including Cauchy's integral theorem and Cauchy's integral formula, which relate the values of complex analytic functions to their behavior along closed contours. These theorems remain fundamental tools in both pure mathematics and theoretical physics.

Cauchy was a devout Catholic and Bourbon royalist who refused to take the oath of allegiance to King Louis-Philippe after the July Revolution of 1830. He went into self-imposed exile, spending time in Turin and later Prague tutoring the grandson of Charles X, before eventually returning to Paris around 1838.