John Bardeen was an American physicist who shared the 1956 Nobel Prize in Physics with William Shockley and Walter Brattain for their development of the transistor. In 1972 Bardeen became the first person to win the physics prize a second time, sharing the award with Leon Cooper and John Schrieffer for their development of a comprehensive theory of superconductivity known as the BCS theory. He worked with the Bell Telephone Laboratories (1945–1951) and was then professor of physics at Illinois University (1951–1971).