19th-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.

Julius August Christoph Zech (24 February 1821 Stuttgart, Germany − 13 July 1864 Berg) was a German astronomer and mathematician.
In 1849, Zech published a table of logarithms; as a result, Zech logarithms for finite fields are named after him.
In 1863, Zech attended the founding meeting of the Astronomische Gesellschaft (German Astronomical Society) and became its Vorstand (chairman). Friedrich Wilhelm Argelander assumed this role upon Zech's death..

Julius Christian Johannes Zeller (24 June 1822, Mühlhausen am Neckar – 31 May 1899, Cannstatt) was a German mathematician. He was born to Gottlob Zeller and Christiana Friedrike Moser.Originally trained in mathematics, geography and theology, in 1874 Zeller became Director of the Seminary in Markgröningen and a girls' orphanage. In 1882 he became a member of the Société Mathématique de France. The following year, on 16 March 1883, he delivered a short account of his congruence relation (Zeller's congruence), which was published in the society's journal.
He was later awarded the Order of Friedrich, First Class, and the Ritterkreuz of Württemberg. He retired in 1898, and died in the following summer.

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

Ludwig Otto Blumenthal (20 July 1876 – 12 November 1944) was a German mathematician and professor at RWTH Aachen University.

Gerhard Hessenberg (German: [ˈgɛʁ.hart ˈhɛsənˌbɛrk]; 16 August 1874 – 16 November 1925) was a German mathematician who worked in projective geometry, differential geometry, and set theory.

Carl August von Steinheil (12 October 1801 – 14 September 1870) was a German physicist, inventor, engineer and astronomer.

Heinrich Carl Franz Emil Timerding (23 January 1873 in Strasbourg – 30 April 1945 in Braunschweig) was a German mathematician, professor at the Braunschweig University of Technology, mainly known for his contributions to probability theory.
He was awarded the Brunswick and the Prussian War Merit Cross, the Ritterkreuz (Knight's Cross) of the Order of Henry the Lion, and in 1938 the Nazi Civil Service Faithful Service Medal.In 1900 he attended Columbia University in New York City the American Mathematical Society's summer meeting, where he read a paper.