Victor Gershevich (Grigorievich) Kac (Russian: Виктор Гершевич (Григорьевич) Кац; born 19 December 1943) is a Soviet and American mathematician at MIT, known for his work in representation theory.
He received the Wigner Medal (1996) "in recognition of work on affine Lie algebras that has had wide influence in theoretical physics".
In 1978 he was an invited speaker (Highest weight representations of infinite dimensional Lie algebras) at the International Congress of Mathematicians (ICM) in Helsinki.
Kac has published 13 books and over 200 articles in mathematics and physics journals and is listed as an ISI highly cited researcher.
Kac and Moody noticed that if Wilhelm Killing's conditions were relaxed, it was still possible to associate to the Cartan matrix a Lie algebra which, necessarily, would be infinite dimensional."