Jean Leray. 7 November 1906 — 10 November 1998

Jean Leray was one of the major mathematicians of the twentieth century. His primary focus in mathematics came from applications; indeed, a majority of his contributions were in the theory of partial differential equations arising in physics, notably his 1934 paper on the Navier–Stokes equation. World War II, during which he was a prisoner–of–war in Austria for five years, induced him to turn to pure mathematics to avoid helping the German war effort. There he worked in topology, developing two radically new ideas: sheaf theory and spectral sequences. After 1950 he came back to partial differential equations and became interested in complex analysis, writing a remarkable series of papers on the Cauchy problem. Leray remained mathematically active until the end of his life; in the course of his career he wrote 132 papers. His influence on present mathematics is tremendous. On the one hand, sheaf theory and spectral sequences became essential tools in contemporary pure mathematics, reaching far beyond their initial scope in topology. On the other hand, Leray can rightly be considered the intellectual guide of the distinguished French school of applied mathematics.