Ursula 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 Communist activist who worked for the Soviet Union in the 1930s and 1940s as a spy, most famously as the handler of nuclear scientist Klaus Fuchs.
She moved to East Germany in 1950 when Fuchs was unmasked, and published a series of books related to her spy work, including her bestselling autobiography, Sonjas Rapport.
Sources concerned with her espionage work in the 1930s/40s sometimes use the cover name originally suggested to her in Shanghai by her fellow intelligence operative Richard Sorge: "Sonja", "Sonja Schultz" or, after she moved to Britain, "Sonya".