Much of the early records of his life come from his own personal accounts and official North Korean government publications, which often conflict with independent sources. Nevertheless, there is some consensus on at least the basic story of his early life, corroborated by witnesses from the period.
Kim was born to
Kim Hyŏng-jik and Kang Pan-sŏk, who gave him the name Kim Sŏng-ju, and had two younger brothers, Ch’ŏl-chu and Yŏng-ju. He was born in Nam-ri, Kophyŏng District, Taedong County,
South P'yŏngan Province (currently the Mangyŏngdae area of
P'yŏngyang), then under Japanese occupation. The ancestral seat (
pon’gwan) of Kim's family is
Chŏnju, North Chŏlla Province, and what little that is known about the family contends that sometime around the time of the Korean-Japanese war of 1592-98, a direct ancestor moved north. The claim may be understood in light of the fact that the early Chosŏn government's policy of populating the north resulted in mass resettlement of southern farmers in Phyŏngan and Hamgyŏng regions in the fifteenth and sixteenth centuries. At any rate, the majority of the Chŏnju Kim, today live in North Korea, and extant Chŏnju Kim genealogies provide spotty records. Moreover, a persistent rumour alleges that during the North Korean occupation of Seoul in the
Korean War, the North Koreans collected all the available Chŏnju Kim genealogies and took them North.
The exact history of Kim's family is somewhat obscure. The family was neither very poor nor comfortably well-off, but was always a step away from poverty. Kim was raised in a Protestant Christian family with strong ties to the church: his maternal grandfather was a Protestant minister, his father had gone to a missionary school, and both his parents were reportedly very active in the religious community. According to the official version, Kim's family participated in Japanese opposition activities, and, in 1920, they fled to Manchuria, where he became fluent in Chinese. The more objective view seems to be that his family settled in Manchuria like many Koreans at the time to escape famine. Nonetheless, Kim’s parents apparently did play a minor role in some activist groups, though whether their cause was missionary, nationalist, or both is unclear.
Kim’s father died in 1926, when Kim was fourteen years old. Kim attended Yulin Middle School in
Jilin, where he rejected the feudal traditions of older generation Koreans and became interested in
communist ideologies; his formal education ended when he was arrested and jailed for subversive activities. At seventeen, Kim had become the youngest member of an underground Marxist organization with less than twenty members, led by Hŏ So, who belonged to the
South Manchurian Communist Youth Association. The police discovered the group three weeks after it was formed in 1929, and jailed Kim for several months.
He joined various anti-Japanese guerrilla groups in northern China, and in 1935 he became a member of the
Northeast Anti-Japanese United Army, a guerrilla group led by the
Communist Party of China. Kim was appointed the same year to serve as political commissar for the 3rd detachment of the second division, around 160 soldiers. It was here that Kim met the man who would become his mentor as a communist,
Wei Zhengmin, Kim’s immediate superior officer, who was serving at the time as chairman of the Political Committee of the Northeast Anti-Japanese United Army. Wei reported directly to
Kang Sheng, a high-ranking party member close to
Mao Zedong in
Yan'an, until Wei's death on
March 8, 1941.
Also in 1935 Kim took the name Kim Il-sung, meaning "become the sun." By the end of the war, this name would be legendary in Korea, and some historians have claimed that it was not Kim Sŏng-ju who originally made the name famous. Soviet propagandist Grigory Mekler, who claims to have prepared Kim to lead North Korea, says that Kim assumed this name while in the Soviet Union in the early 1940s from a former commander who had died.
On the other hand, some Koreans simply did not believe that someone as young as Kim could have anything to do with the legend. Historian
Andrei Lankov has claimed that the rumor Kim Il Sung was somehow switched with the “original” Kim is unlikely to be true. Several witnesses knew Kim before and after his time in the Soviet Union, including his superior,
Zhou Baozhong, who dismissed the claim of a “second” Kim in his diaries.
Kim was appointed commander of the 6th division in 1937, at the age of 24, controlling a few hundred men in a group that came to be known as “Kim Il Sung’s division.” It was while he was in command of this division that he executed a raid on
Poch’onbo, on
June 4. Although Kim’s division only captured a small Japanese-held town just across the Korean border for a few hours, it was nonetheless considered a military success at this time, when the guerrilla units had experienced difficulty in capturing any enemy territory. This accomplishment would grant Kim some measure of fame among Chinese guerrillas, and North Korean biographies would later exploit as a great victory for Korea. Kim was appointed commander of the 2nd operational region for the 1st Army, but by the end of 1940, he was the only 1st Army leader still alive. Pursued by Japanese troops, Kim and what remained of his army escaped by crossing the
Amur river into the
Soviet Union. Kim was sent to a camp near
Khabarovsk, where the Korean Communist guerrillas were retrained by the Soviets. Kim became a
Captain in the Soviet
Red Army and served in it until the end of World War II.
The
Communist Party of Korea had been founded in 1925, but had soon been disbanded due to internal strife. In 1931, Kim had joined the
Communist Party of China. When he returned to Korea, in September 1945, with the Soviet forces, he was installed by the Soviets as head of the Provisional People's Committee. He was not, at this time, the head of the Communist Party, whose headquarters were in
Seoul in the
U.S.-occupied south. During his early years as leader, he assumed a position of influence largely due to the backing of the Korean population which was supportive of his fight against Japanese occupation.
One of Kim's most lasting accomplishments was his establishment of a professional army, the
North Korean People's Army (NKPA), formed from a cadre of guerrillas and former soldiers who had gained combat experience in battles against the Japanese and later
Nationalist Chinese troops. From their ranks, using Soviet advisers and equipment, Kim constructed a large army skilled in infiltration tactics and guerrilla warfare. Before the outbreak of the Korean War,
Joseph Stalin equipped the NKPA with modern heavy tanks, trucks, artillery, and small arms (at the time, the South Korean Army had nothing remotely comparable either in numbers of troops or equipment). Kim also formed an air force, equipped at first with ex-Soviet propeller-driven fighter and attack aircraft. Later, North Korean pilot candidates were sent to the Soviet Union and China to train in
MiG-15 jet aircraft at secret bases.