Swedish mathematician who was awarded the Fields Medal in 1962 for his work on partial differential equations. Between 1987 and 1990 he served as a vice president of the International Mathematical Union. In 1988 Hörmander was awarded the Wolf Prize.

Hörmander attended the University of Lund, Sweden. He held appointments at Lund (1955–57), Stockholm University (1957–64), and Stanford University, Calif., U.S. (1963–64). Following research at the Institute for Advanced Study, Princeton, N.J. (1964–68), he returned to Lund in 1968.

Hörmander was awarded the Fields Medal at the International Congress of Mathematicians in Stockholm in 1962. Among his more notable achievements was his establishment of a theory of distributions using Fourier analysis. This is an extension of Laurent Schwartz's concept of a “distribution,” (Schwartz, Laurent) with which he brought rigour to the examination of mass distributions. Hörmander was also one of the principal contributors to the development of the theory of pseudo-differential operators, which grew out of the theory of linear partial differential operators and the study of singular integral operators.

Hörmander's publications include Linear Partial Differential Operators (1963); An Introduction to Complex Analysis in Several Variables (1966); Implicit Function Theorems (1977); General Pseudo-Differential Operators (1977); The Analysis of Linear Partial Differential Operators, 4 vol. (1983–90); and Notions of Convexity (1994).