Georg Cantor (1845- 1918), German mathematician. Born in St. Petersburg, Russia, Cantor studied in Berlin, Germany, before becoming Professor of Mathematics at Halle in 1877. He did important work on classical analysis, using Fourier series to develop a theory of irrational numbers. Cantor formulated the theory of sets, upon which modern mathematical analysis is based. His theory extended number theory by introducing infinite numbers. Cantor's work led to subsequent investigations of the foundations of mathematics and mathematical logic.