Isaac Folkoff was a senior member of the California Communist Party and West Coast liaison between Soviet intelligence and the Communist Party of the United States of America (CPUSA). Folkoff was in charge of West Coast operations. Folkoff worked as a courier passing information to and from Soviet sources, and as a talent spotter and vetter of potential espionage recruits. He also worked as a case officer. His code name in Soviet intelligence and in the Venona files was "Uncle".
Folkoff collected CPUSA dues from J. Robert Oppenheimer who had been an ardent Popular Front liberal and ally. Folkoff collected 150 dollars a month from Oppenheimer. As director of the Manhattan Project Oppenheimer knew all the secrets, and just as soon as new secrets came into being. Up to the time Oppenheimer reported his contact with Haakon Chevalier, he may have overlooked the conduct of others, a passivity motivated by personal and political ties. Another theory states Chevalier's approach To Oppenheimer may not have been an attempt at recruitment, but part of the big shake up after Stalin publicly disbanded the Comintern in 1943, and agents had to be reassigned new case officers. Oppenheimer is mentioned in a KGB communication:
- In 1942 one of the leaders of scientific work on uranium in the USA, Professor R. Oppenheimer while being an unlisted [nglastny] member of the apparatus of Comrade Browder informed us about the beginning of work. On the request of Kheifetz, confirmed by Comrade Browder, he provided cooperation in access to research for several of our tested sources including a relative of Comrade Browder...Due to complications…it is expedient to immediately sever contacts of leaders and activist of the American Communist Party with scientists and specialists engaged in work on uranium. 
- Jerrold L. Schecter and Leona Schecter, Sacred Secrets: How Soviet Intelligence Operations Changed American History (Washington, DC: Brassey’s, 2002) FBI document attesting to that in Appendix 1.
- John Earl Haynes and Harvey Klehr, Venona: Decoding Soviet Espionage in America, Yale University Press, 1999, pp. 327-330.
- Sacred Secrets p. 50.