Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Oskar Benjamin Klein (September 15, 1894 - February 5, 1977) was a Swedish theoretical physicist. Klein was born in Danderyd outside Stockholm, son of the chief rabbi of Stockholm, Dr. Gottlieb Klein and Antonie (Toni) Levy. He became a student of Svante Arrhenius at the Nobel Institute at a young age, and was on the way to Jean-Baptiste Perrin in France when World War I broke out and he was drafted into the military. From 1917 he worked a few years with Niels Bohr in Copenhagen and received his doctoral degree at the University College of Stockholm (now Stockholm University) in 1921.