Annen (841? - 915?) was a Buddhist monk of Tendai Sect in the early Heian period. He was also called Godaiin Ajari (a master in esoteric Buddhism; a high priest), Akaku Daishi, Fukushu Kongo or Shinnyo Kongo. He was born in Omi Province. His family line is not clear but it is believed that he belonged to the same clan as Saicho.
He studied Kenmitsu Buddhism (Exoteric Buddhism and Esoteric Buddhism), kai (precept) and siddham (Sanskrit) initially under Dengyo Daishi Ennin and after his death, under Hensho. He tried to travel to China (Tang) in 877 but gave up. He became Ajari and assumed the position of the head priest of Gankei-ji Temple in 884. In his later years, he established Godaiin at Mt. Hiei and concentrated in the studies of Tendai Buddhism and Esoteric Buddhism.