Lars Valter Hörmander (born 24 January 1931) is a Swedish mathematician and one of the leading experts in partial differential equations. He was awarded the Fields Medal in 1962, and the Wolf Prize in 1988. His Analysis of Linear Partial Differential Operators I - IV is considered a standard work on the subject of linear partial differential operators. He was vice president of the International Mathematical Union between 1987 and 1990.

Hörmander was born in Mjällby, a village in Blechingia in southern Sweden. In 1948 he graduated from the gymnasium in Lund, where he had been given a chance to study university level mathematics. He attended Lund University and received a Master's degree in 1950. He completed his Ph.D. in 1955.

Between 1955 and 1957, he visited various universities in the United States. He was given professorship at the University of Stockholm in 1957. During the following years he switched location several times between Stockholm and universities in the United States, particularly the Institute for Advanced Study and Stanford University. He returned to Lund in 1986, where he is a professor emeritus since 1996.