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Ursula Ruth Kuczynski (15 May 1907, Schöneberg, Prussia, German Empire – 7 July 2000, Berlin, Germany, also known as Ruth Werner, Ursula Beurton and Ursula Hamburger) was a German author and spy for the Soviet Union. A daughter of Robert René Kuczynski, she joined the Communist Party of Germany at an early age. After her family moved to the United States in 1928, Kuczynski became a spy for the GRU. Code-named "Sonja", she married Rudolf Hamburger, another GRU agent, and moved to China, where she operated a spy ring under the direction of Richard Sorge. 
After undergoing formal training in Moscow in 1934, she was active in Manchuria in 1935, then moved to London before going to Switzerland in 1939, where she collaborated with the Lucy spy ring. She divorced later that same year, and remarried with Len Beurton shortly afterwards. In 1941 she moved to Britain and continued her activities for the GRU for most of the decade. A member of her network was the physicist Klaus Fuchs. 
Following the arrest of Fuchs in late 1949, Kuczynski fled to East Berlin, where she retired from the GRU in 1950.
After her resignation, she worked for the East German government for a decade, then began a new career as an author. Her writings include her autobiography, Sonja's Report and several children's books.
She was awarded the Order of the Red Banner twice in recognition to her services to the Soviet Union, in 1937 and 1969.
- Biography of Ursula Beurton
- Mitrokhin Archive (Volume 7, Chapter 14)
- The Spy Museum, 2007
- Richard C.S. Trahair. Encyclopedia of Cold War Espionage, Spies and Secret Operations. Greenwood Press, Westport, Connecticut – London 2004, p. 156. ISBN 0-313-31955-3
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