20th-century German mathematicians

Felix Christian Klein (German: [klaɪn]; 25 April 1849 – 22 June 1925) was a German mathematician and mathematics educator, known for his work in group theory, complex analysis, non-Euclidean geometry, and the associations between geometry and group theory. His 1872 Erlangen program classified geometries by their basic symmetry groups and was an influential synthesis of much of the mathematics of the time.
During his tenure at the University of Göttingen, Klein was able to turn it into a center for mathematical and scientific research through the establishment of new lectures, professorships, and institutes. His seminars covered most areas of mathematics then known as well as their applications. Klein also devoted considerable time to mathematical instruction, and promoted mathematics education reform at all grade levels in Germany and abroad. He became the first president of the International Commission on Mathematical Instruction in 1908 at the Fourth International Congress of Mathematicians in Rome.

Hans Heinrich Wilhelm Magnus known as Wilhelm Magnus (5 February 1907 in Berlin, Germany – 15 October 1990 in New Rochelle, New York) was a German-American mathematician. He made important contributions in combinatorial group theory, Lie algebras, mathematical physics, elliptic functions, and the study of tessellations.

Ludwig Otto Hölder (December 22, 1859 – August 29, 1937) was a German mathematician born in Stuttgart.

Käte Fenchel née Käte Sperling (21 December 1905 – 19 December 1983) was a German-born Jewish mathematician, best known for her work on non-abelian groups.

Richard Rado FRS (28 April 1906 – 23 December 1989) was a German-born British mathematician whose research concerned combinatorics and graph theory. He was Jewish and left Germany to escape Nazi persecution. He earned two PhDs: in 1933 from the University of Berlin, and in 1935 from the University of Cambridge. He was interviewed in Berlin by Lord Cherwell for a scholarship given by the chemist Sir Robert Mond which provided financial support to study at Cambridge. After he was awarded the scholarship, Rado and his wife left for the UK in 1933. He was appointed Professor of Mathematics at the University of Reading in 1954 and remained there until he retired in 1971.

Reinhold Strassmann (or Straßmann) (24 January 1893 in Berlin – late October 1944 in Auschwitz concentration camp) was a German mathematician who proved Strassmann's theorem. His Ph.D. advisor at University of Marburg was Kurt Hensel.
Born into a Jewish family, Strassmann refused to leave Nazi Germany, and he was eventually detained and deported to Theresienstadt concentration camp in 1943. On October 23, 1944, he was deported from Theresienstadt to Auschwitz concentration camp, where he was murdered soon after.He was the son of the forensic pathologist Fritz Strassmann.

Robert Erich Remak (14 February 1888 – 13 November 1942) was a German mathematician. He is chiefly remembered for his work in group theory (Remak decomposition). His other interests included algebraic number theory, mathematical economics and geometry of numbers. Robert Remak was the son of the neurologist Ernst Julius Remak and the grandson of the embryologist Robert Remak. He was murdered in the Holocaust.

Konrad Hermann Theodor Knopp (22 July 1882 – 20 April 1957) was a German mathematician who worked on generalized limits and complex functions.

Ernst Erich Jacobsthal (16 October 1882, Berlin – 6 February 1965, Überlingen) was a German mathematician, and brother to the archaeologist Paul Jacobsthal.
In 1906, he earned his PhD at the University of Berlin, where he was a student of Georg Frobenius, Hermann Schwarz and Issai Schur; his dissertation, Anwendung einer Formel aus der Theorie der quadratischen Reste (Application of a Formula from the Theory of Quadratic Residues), provided a proof that prime numbers of the form 4n + 1 are the sum of two square numbers. In 1934, he was fired from his professorship at the Technische Hochschule Berlin, because of his Jewish origins. In 1939 he fled to Norway and became after the war a professor at the Norwegian Institute of Technology in Trondheim.

Hans Ludwig Hamburger (5 August 1889, Berlin – 14 August 1956, Cologne) was a German mathematician. He was a professor at universities in Berlin, Cologne and Ankara.