Kakuun (953 - December 18, 1007) was a Buddhist priest of the Tendai sect who lived in the mid-Heian period. His father was FUJIWARA no Sadamasa, a Togu-shoshin (official of the Crown Prince's Quarters).
Kakuun studied Tendai doctrine under Ryogen at a temple on Mt. Hiei. He became distinguished for his learning, and he conducted kosetsu (lectures such as those on the Buddhist scriptures) eagerly at the Toto (of Enryaku-ji Temple) Danna-in Temple, where he dwelled. Upon the advice of Ryogen, he studied Shingon Esoteric Buddhism from Joshin and Kokei. As he gained the favor of the Imperial Court and nobles, he lectured to FUJIWARA no Michinaga on the Makashikan (the Mahayana practice of cessation and contemplation) and so on, lectured to Emperor Ichijo on the Hokkesho (annotation of the Lotus Sutra), and he concerned himself with various Buddhist rites relating to the family of FUJIWARA no Michinaga. In 1003, he was appointed as the Gon no Shosozu (a provisional junior rank in the second-highest position of priest), and later Gon dai sozu (the provisional second-highest position, upper grade, of priest). Although he passed away in 1007, he was appointed as the Gonsojo (the lowest grade that can be held by one who has reached the highest rank in the hierarchy of Buddhist priests) after his death. In later ages, it was said that Kakuun was the originator of the Danna school, just as it was said that Genshin originated the Eshin school.