Walter Feit (October 26, 1930 – July 29, 2004) was an American mathematician who worked in finite group theory and representation theory.
He was born in Vienna and left for England in 1939. He moved to the United States in 1946 where he became an undergraduate at the University of Chicago. He did his Ph.D. at the University of Michigan, and became a professor at Cornell in 1952, and at Yale in 1964.
His most famous result is his joint, with John G. Thompson, proof of the Feit–Thompson theorem that all finite groups of odd order are solvable. At the time it was written, it was probably the most complicated and difficult mathematical proof ever completed. He wrote almost a hundred other papers, mostly on finite group theory, character theory (in particular introducing the concept of a coherent set of characters), and modular representation theory. Another regular theme in his research was the study of linear groups of small degree, that is, finite groups of matrices in low dimensions. It was often the case that, while the conclusions concerned groups of complex matrices, the techniques employed were from modular representation theory.
He also wrote the books: The representation theory of finite groups and Characters of finite groups, which are now standard references on character theory, including treatments of modular representations and modular characters.
He was awarded the Cole Prize by the American Mathematical Society in 1965, and was elected to the United States National Academy of Sciences and the American Academy of Arts and Sciences. He also served as Vice-President of the International Mathematical Union.