Felix Klein

German mathematician, author of the Erlangen Program
Felix Christian Klein

Felix Christian Klein (April 25, 1849, Düsseldorf, (then) Prussian EmpireJune 22, 1925, Göttingen, Germany) was a German mathematician. He became known for his work in group theory, function theory, non-Euclidean geometry, and on the connections between geometry and group theory. His 1872 Erlangen Program, which ate geometries by their underlying symmetry groups, was a hugely influential synthesis of much of the mathematics of the day.

The Klein bottle is named after him.