Sergey Nikolaevich Kurnakov or Sergei N. Kournakoff (Russian: Сергей Курнаков; 1892 – 1949) was a former tsarist cavalry officer who had immigrated to the U.S. and later became an ardent ideological Communist.
He subsequently emigrated to America and became a journalist who wrote on military affairs for the Communist Party of the United States of America (CPUSA) paper, the Daily Worker, and other publications Kurnakov served as a courier to various Soviet intelligence sources, and acted as both a talent-spotter and a vetter of potential recruits.
Kurnakov also took over Mary Jane Keeney who worked for the Board of Economic Warfare and later the United Nations from Soviet Military Intelligence (GRU).
At their first meeting, Hall gave Kurnakov a report he had prepared on the Los Alamos facility, the progress of the research, and the roles of the chief scientists working on the atomic bomb.
Kurnakov immediately reported to KGB Officers Anatoly Yatskov and Stepan Apresyan on his meeting with Hall.