Kim Philby

The "third man" of the so-called " Cambridge spy ring" -- a devoted British communist and one of the most damaging moles in the history of Western intelligence. Schooled at Cambridge University, where he came in contact with fellow Soviet spies Guy Burgess, Donald Maclean and Anthony Blunt, Philby entered the British Secret Intelligence Service (MI-6), rising to highly sensitive positions. After World War II he became head of counterespionage operations; in 1949 he was named chief MI-6 officer in Washington and top liaison officer between British and U.S. intelligence services. Here, Philby kept the Soviets well apprised of the operations of both agencies. He is thought responsible for the deaths of many Western agents he betrayed to the Soviets.

His association with fellow double-agents Burgess and Maclean -- whom he helped escape to the Soviet Union -- eventually led to his downfall. Under suspicion, he was relieved of his intelligence duties in 1951 and dismissed from MI-6 in 1955. In 1963 he fled to the Soviet Union , where he joined the KGB. When he died in 1988, he was buried with full honors in a Moscow cemetery.