Tian Kehan (Chinese: 天可汗; pinyin: Tiān Kěhán; Wade–Giles: T'ien K'ehan) also translated as Heavenly Khagan, Celestial Khagan or Tengri Khagan, was a title addressed to Emperor Taizong of Tang by various Turkic nomads. It was first mentioned in accounts on May 20, 630 and again on October 24, 646, shortly after the Eastern Turkic Khaganate and Xueyantuo were annihilated by Emperor Taizong's generals.
The title Tengri Khagan also used to refer another two Turkic ruler, both known as the Dengli Khagan to the Chinese, during the Second Eastern Turkic Khaganate (r. 739–741) and Uyghur Khaganate (r. 759–779) periods.
It is not certain whether the title also applied to the rest of the Tang emperors, or to the empress Wu Zetian, since the term "Kaghan" only referred to male rulers and Empress Wu had started her dominion in the Chinese court after the year 665 AD until the year 705 AD, which is after the title's first use by a Chinese emperor. However, we do have two appeal letters from the Turkic hybrid rulers, Ashina Qutluγ Ton Tardu in 727, the Yabgu of Tokharistan, and Yina Tudun Qule in 741, the king of Tashkent, addressing Emperor Xuanzong of Tang Li Longji as Tian Kehan during the Umayyad expansion.
A later letter sent by the Tang court to the Yenisei Kirghiz Qaghan explained that "the peoples of the northwest" had requested Tang Taizong to become the "Heavenly Qaghan".