Paul Julius Oswald Teichmüller (German: [ˈɔsvalt ˈtaɪçmʏlɐ]; 18 June 1913 – 11 September 1943) was a German mathematician who made contributions to complex analysis. He introduced quasiconformal mappings and differential geometric methods into the study of Riemann surfaces. Teichmüller spaces are named after him. Sanford L. Segal, a professor of mathematics at the University of Rochester, in his 2003 book Mathematicians Under the Nazis said: "Teichmüller was a gifted, brilliant, and seminal mathematician; he was also a dedicated Nazi."