Stephan Cohn-Vossen

Stefan Cohn-Vossen was a mathematician, specializing in differential geometry. He is best known for his collaboration with David Hilbert on the 1932 book Anschauliche Geometrie, translated into English as Geometry and the Imagination. Both Cohn-Vossen's inequality and the Cohn-Vossen transformation are named after him. He also proved the first version of the splitting theorem.