Description: (Cipher clerk known for exposing Joseph Stalin's efforts to steal nuclear secrets)
Igor Sergeyevich Gouzenko, a cipher clerk for the Soviet embassy in Canada and a lieutenant of the Soviet Main Intelligence Directorate (GRU), defected in 1945 after World War II. He brought with him 109 documents that revealed the USSR's espionage activities in the West. Gouzenko's revelations exposed Soviet intelligence's efforts to steal nuclear secrets and deploy sleeper agents, marking a crucial turning point in the beginning of the Cold War. His actions raised public awareness about the threats posed by Soviet espionage.