Klaus Fuchs, a physicist and mathematician, fled Germany after the Nazis came to power in 1933 and ended up in Great Britain. He began passing secret research material to the Soviet Union. His espionage activities were detected in 1950 and he was later sentenced to 14 years in prison. In 1959, Fuchs was released from prison and moved to East Germany.
Richert, Lucas Paul. "Klaus Fuchs convicted of passing atomic secrets to Russia". The Literary Encyclopedia. First published 01 October 2008
[http://www.litencyc.com/php/stopics.php?rec=true&UID=3215, accessed 23 September 2014.]