Kul Tegin was born in 684. When his father Ilteris died, his elder brother Bilge was 8, and Kul Tegin was 7. He was brought up by his uncle Kapagan Khan, together with his brother. When Bilge Khan ascended the throne when he was 32, Kul Tegin became his 31-year-old assistant and commanded the army. The most accurate information about Kul Tegin, who put down the rebellions in the country with his elder brother, are in Orhun Memorials. Kul Tegin attended the war against Chinese army consisting of 50 thousand people when he was 16, together with his uncle Kapagan Khan, and attracted interest with his heroism. Kul Tegin, also took part in the war against Chinese General Caca when he was 21, and lost his three horses. It is written in the memorials that he saved himself from more than 100 arrows shot by Chinese soldiers and had an important role in winning of the war.
Kul Tegin took part in the campaign against Kirghizes rising against Gokturk State, when he was 26. In the war in 710 on the foot of Sanga mountain, his fight attracted attention of Chinese and he was indicated as "Undefeatable Warrior" in Chinese sources.
Kul Tegin died on 27 February 731 when he was 47. A big funeral ceremony was arranged for him on 1 November 731. In his funeral, there were Chinese, Titan, Tatabi, Tibet, Iran, Sogd, Bukhara, Turgis, Kirghiz and other state clans.