Tenkai was born in 1536. His childhood name was Heitaro, and he later went by such names as Zuifu and Nankobo; after his death he was given the title Jigen Daishi. He is said to have been bom in the province of Aizu, present-day Fukushima Prefecture.
At an early age he entered a local temple called the Ryuko-ji and began the study and practice of Buddhism. In time he made his way to the Enryaku-ji and Onjo-ji (Miidera), the two principal temples on Mt. Iliei, the headquarters of the Tendai sect, and later went to the Kofuku-ji in Nara for further study. In 1560 he entered the Ashikaga School in Kozuke Province, where he devoted himself to the study of Confucianism.
In 1590 he went to study under a priest named Gokai of the Muryoju-ji in Kawagoe Semba in Musashi Province, and in honor of his teacher changed his name to Tenkai.
In 1589 he had his first interview with Tokugawa Ieyasu at Edo Castle and won the confidence of the future founder of the Tokugawa shogunate.
In 1599 he was assigned a temple of his own, the Kita-in in Kawagoe Semba. In 1613 Ieyasu made him head of the Nikko-san, an important Tendai temple at Nikko in Shimotsuke. After the death of Ieyasu in 1616, he journeyed to Kyoto to ask the emperor to bestow a posthumous title upon Ieyasu. At the same time he himself was raised to the position of daisojo, the highest ecclesiastical rank. In 1617 he removed the body of Ieyasu from its temporary burial place at Mt. Kuno in Suruga and escorted it for reburial to Nikko. In 1624 at the command of the second shogun, Tokugawa Hidetada, he founded the Tendai temple known as the Toei-zan Kan’ei-ji on a hill called Shinobugaoka in the Ueno section of Edo. During his lifetime he enjoyed the confidence of three shoguns, from Ieyasu to Iemitsu, and played an important role as an advisor to the government on both foreign and domestic affairs.
In 1637 he began the printing of a new edition of the Daizokyo (Tripitaka), which came to be lmown as the Tenkai Edition, but died at the age of 107 before the undertaking was completed.
