Felix Klein — German Mathematician born on April 25, 1849, died on June 22, 1925
Christian Felix Klein was a German mathematician and mathematics educator, known for his work in group theory, complex analysis, non-Euclidean geometry, and on the connections between geometry and group theory. His 1872 Erlangen Program, classifying geometries by their underlying symmetry groups, was a hugely influential synthesis of much of the mathematics of the day... (wikipedia)