 He was born presumably in 1920 to a poor peasant family in Kumya County, South Hamgyong Province, during the Japanese rule and, like many other young Koreans, he joined the Imperial Japanese Army in Manchukuo.At first serving in the military police, he soon became a reputed detective whose job was to uncover moles in the Japanese intelligence service and to hunt communists.In 1941, Kim cunningly assumed the appearance of a beggar to get close to Wang Gunlai (王近禮), an infamous Chinese spymaster.