Born in 626, son of Emperor Jomei and Empress Kogyoku. Growing alarmed at Soga tyranny, he secretly conspired with Nakatomi no Kamatari to bring down the clan. In 645 at Asuka Itabuki Palace, he personally struck Soga no Iruka with his sword in the Isshi Incident, destroying the Soga main line. As crown prince under Emperor Kotoku, he held real power and drove the Taika Reform—establishing public land and people systems, land allotment, and the national provincial system. After crushing defeat at the Battle of Baekgang (663), he reinforced coastal defenses, built water fortifications, and instituted the Sakimori frontier guard. Ascending as Emperor Tenji in 668, he moved the capital to Otsu, compiled early legal codes, and conducted Japan's first nationwide census in 670. He died in 671 without clearly naming a successor, triggering the Jinshin War between rival claimants the following year.

Decisive and ruthless. Showed bold action by personally drawing his sword against the Soga. Displayed superb leadership in reform and rapid defense-building after the Baekgang defeat.

Laid the foundation of Japan's centralized state through the Taika Reform. Also known as the author of the opening poem of the Hyakunin Isshu. The succession dispute after his death led to the Jinshin War, the greatest civil war in ancient Japan.