Klaus Fuchs (1911 - 1988)
Klaus Fuchs, a British scientist in the theoretical division at Los Alamos during the Manhattan Project, had access to top secret material, much of which he passed to the Soviets. The Soviet atomic bomb project was greatly aided by the information given to them. Fuchs was tried and convicted in Britain in the 1950s. Fuchs served 9 years of a 14 year sentence. He then emigrated to East Germany.