Igor Sergeyevich Gouzenko (Russian: ????? ????????? ??????? ['ig?r? s??r'g?ej?v??t? g?'z??nk?]; January 26, 1919 – June 25, 1982) was a cipher clerk for the Soviet embassy to Canada in Ottawa, Ontario.
He defected on 5 September 1945, three days after the end of World War II, with 109 documents on the USSR's espionage activities in the West.
This forced Canada's Prime Minister Mackenzie King to call a Royal Commission to investigate espionage in Canada.
Gouzenko exposed Soviet intelligence' efforts to steal nuclear secrets as well as the technique of planting sleeper agents.
The "Gouzenko Affair" is often credited as a triggering event of the Cold War, with historian Jack Granatstein stating it was "the beginning of the Cold War for public opinion" and journalist Robert Fulford writing he was "absolutely certain the Cold War began in Ottawa".
Granville Hicks described Gouzenko's actions as having "awakened the people of North America to the magnitude and the danger of Soviet espionage".