Felix Klein was a German mathematician born on April 25, 1849, and he is best known for his work in geometry and group theory. He introduced the Klein bottle, a non-orientable surface that challenges traditional notions of dimensions. Klein also contributed to the development of Klein's quartic, a complex algebraic curve that has interesting properties in mathematics. In addition to his mathematical discoveries, Klein was an influential educator. He served as a professor at various universities, including the University of Göttingen. Klein was also involved in the establishment of the Mathematical Society of Göttingen, promoting collaboration and research in mathematics during the late 19th century.