Marika Rökk, whose career in German cinema spanned from the 30s to the late 80s, was a spy for the Soviet Union during WW2, and perhaps later, according to The Guardian.
Star of postwar German cinema was Soviet spy, declassified files show
One of Germany’s best-loved postwar actors has been exposed as a Soviet agent following the declassification of top secret intelligence documents.
Marika Rökk, who was banned from acting for two years for her apparent closeness to the Nazi regime, had in fact been working from the 1940s onwards for a reconnaissance network passing Third Reich secrets to Moscow.
...
It is believed she was recruited as a KGB agent by her manager, Heinz Hoffmeister, who was already working for Soviet intelligence. What Rökk’s role was, and specifically what information she might have passed on to Moscow, remains unclear.
The article goes on to say that she was reportedly one of Hitler's favourite actors, and that she may have had an affair with Goebbels! She had been uncovered by the Gehlen Organisation in 1951, although the matter was covered up for unspecified reasons.
Soviet espionage in Germany during the Second World War was extensive and very effective. Though Stalin didn't always ~ahem~ make the best use of the material.
While much has been written about the Rotte Capelle (Red Orchestra) network in Berlin, the alleged circuit that Rökk belonged to—Krona—has had less attention. This story of her handler, Yan Chernyak, is fascinating, if it is to be believed. (Note the source.)
The man who handed the USSR the Nazi plans for Barbarossa and Kursk
This network of agents included an important banker, a minister's secretary, the head of the research department of an airplane construction company, the daughter of a director of a tank construction company and high-ranking military officials. And some of the agents who have by now been uncovered were Hitler's favorite actresses Marika Rökk and Olga Chekhova.
In 1941 Chernyak's informers were able to get hold of a copy of the Barbarossa plan and in 1943 – the operative plan of Germany's invasion of Kursk. Although in 1941 Moscow did not take into consideration the unique documents that the agent had sent, resulting in the USSR being caught by surprise when the Germans attacked, in 1943 his multipage reports helped to destroy the Nazi hordes near Belgorod and Kursk, as well as launch the decisive turnaround in the war on the Eastern Front.
Additionally, Chernyak used to give the USSR valuable technical information on the German Tiger and Panther tanks, artillery weapons, rocket weapons, the FAU-1 and FAU-2 rockets, chemical weapons developments and electronic systems.
I'm skeptical of the claim that he made his way to the US and Canada, and that he had any involvement with the atomic weapons spying. I don't recall seeing any mention of him from Igor Gouzenko, the cipher clerk who defected from the Soviet Embassy in Ottawa in 1945.
Oddly, the Guardian article states that an (unreferenced) article in the Bild newspaper first mentioned the declassified material. However, the story above also names Rökk, but it is dated from last May.