Max Dehn

Max Wilhelm Dehn (13 November 1878 to 27 June 1952) was a German mathematician most famous for his work in geometry, topology and geometric group theory. He was born to a family of Jewish origin in Hamburg and studied the foundations of geometry with David Hilbert at Göttingen in 1899, obtaining a proof of the Jordan curve theorem for polygons. In 1900 he wrote his dissertation on the role of the Legendre angle sum theorem in axiomatic geometry, constructing the Dehn planes as counterexamples, and in his habilitation in 1900 he resolved Hilbert's third problem, the first of Hilbert's 23 problems to be resolved. He was forced to retire in 1935, fled Germany in 1939 and emigrated to the United States. His doctoral students include Ott-Heinrich Keller, Ruth Moufang and Wilhelm Magnus.