Though believed to have been born in Aizu, much of Tenkai's early life is unclear.He became a monk at
Ryūkō-ji Temple, adopting the name
Zuihū. At age 14, he studied Tendai Buddhism under Kōshun (皇舜) at Konokawa-dera in Utsunomiya, Shimotsuke Province. He then pursued further studies at
Enryaku-ji on Mount Hiei in Ōmi Province, Onjō-ji, and Kōfuku-ji in Yamato Province. In 1571, when
Oda Nobunaga attacked and burned Mount Hiei, Tenkai took refuge in Kai Province at the invitation of Takeda Shingen. Later, he moved to Inari-dō Hall in Kurokawa Castle (Wakamatsu Castle) under Ashina Morikatsu's invitation. Afterward, he resided at Chōraku-ji Temple in Kōzuke Province before moving to the North Hall of Muryōju-ji Temple (now Kita-in in Kawagoe, Saitama) in 1588, where he adopted the name
Tenkai. Tenkai's activities become more prominent after arriving at the North Hall of Muryōju-ji. At this time, he also served as abbot of Edosaki Fudō-in. According to records from Sensō-ji Temple, Tenkai was present in
Tokugawa Ieyasu's camp during the Siege of the
Hōjō clan, indicating he had originally come to the Kantō region on Ieyasu's behalf. In 1599, Tenkai succeeded Gōkai as the abbot of the North Hall. He later acted as Ieyasu's advisor in negotiations with the Imperial Court and was appointed Tendai Overseer in 1607, residing at Nankōbō and working on the restoration of Enryaku-ji. In 1609, he was appointed Deputy Prelate. In 1612, Tenkai began rebuilding the North Hall and renamed it
Kita-in, establishing it as the main temple of the Kantō Tendai branch. In 1613, Ieyasu appointed him Abbot of Nikkō-zan, where he restored the main temple, Kōmyō-in. He was also heavily involved in the
Hōkō-ji Bell Incident, which contributed to the outbreak of the Siege of Osaka. In 1616, when Ieyasu was on his deathbed, he entrusted Tenkai with instructions regarding his posthumous title and funeral. After Ieyasu's death, Tenkai advocated for Ieyasu to be enshrined as
Gongen in the Sannō Ichijitsu Shintō tradition, countering the proposal by Ishin Sūden and Honda Masazumi, who suggested the title
Myōjin. Tenkai argued that
Myōjin was inauspicious due to the fall of the Toyotomi clan following Toyotomi Hideyoshi's enshrinement as
Toyokuni Daimyōjin. Ultimately, Ieyasu was enshrined as
Tōshō Daigongen, and his remains were moved from Kunōzan to Nikkō. Tenkai continued to serve as a consultant to the next two
Tokugawa shōguns. In 1624, retired shōgun
Tokugawa Hidetada and ruling shōgun
Tokugawa Iemitsu asked him to establish
Kan'ei-ji, a Buddhist temple to the northeast of
Edo Castle in
Ueno. Tenkai worked to print and publish the entire Buddhist Canon in Japan. With shogunate support, the ''Kan'ei-ji Edition
(Tenkai Edition) of the Tripiṭaka'' was completed in 1648. This printing project is considered one of the most significant achievements in Japanese printing history. Over 260,000 wooden movable type blocks from the Tenkai Edition still survive today. Tenkai died in 1643 at the age of 108 (by traditional count). Five years later, the Imperial Court granted him the posthumous title
Jigan Daishi. == In popular media ==