Lie, (Marius) Sophus[lee]
Mathematician, born in Nordfjordeide, Norway. He studied at Oslo University, then supported himself by giving private lessons. He became professor of mathematics at Oslo, then succeeded Felix Klein at Leipzig (1886), and returned to Oslo in 1898. His study of contact transformations arising from partial differential equations led him to develop an extensive theory of continuous groups of transformations, now known as Lie groups. This theory has become a central part of 20th-c mathematics, and has important applications in quantum theory.