Gien (aka Giin; year of birth unknown - November 29, 728) was a priest of Hosso sect of Buddhism (Japanese equivalent of the Chinese Faxiang sect or Dharma-character school), who lived in the Nara period. According to "Shoku Nihongi" (literally, Chronicle of Japan Continued, which is the second of the six classical Japanese history texts), his secular surname was Ichiki, but in "Fuso ryakki" (literally, A Short History of Japan) he appears as born in Takaichi no kori (or Takaichi-gun) County in Yamato Province under the clan name of Ato.
It is said that for many years his parents had prayed for a blessing before an image of the Kannon Buddhist, deity of mercy, so that they were finally blessed with a baby who was Gien, and under Emperor Tenmu's command he was brought up along with the imperial princes at Okamoto no miya Palace. He entered the Buddhist priesthood at Gango-ji Temple where he studied vijnapti-matrata or Consciousness-only school (aka Yuishiki or wei shih, i.e. a theory that all existence is subjective and nothing exists outside of the mind) and dharmalaksana or Dharma-character school (aka Hosso or faxiang, i.e. the specific characteristics of all manifest phenomena), and founded the gokaryu-ji (literally, the five Ryu [dragon] temples) including Ryugai-ji (aka Oka-dera) Temple. In 699, he received an religious studies academic prize of 10,000 sheaves of rice and, in 703, was appointed as a sojo (high-priest). He attended to Empress Gensho and Emperor Shomu at the imperial palace as a naigubu (inner offerer which was any of the 10 high-ranking monks serving at the inner offering hall). The "Shoku Nihongi" indicates that the Emperor extolled him for what he had done since the time of the previous emperor, he was granted the family name Oka no muraji and graciously permitted to share it with his siblings.
According to "Sangoku Buppo Denzu Engi" (literally, History of the transmission and propagation of Buddhism in the three countries), his pupils included Genbo, Gyoki, Ryuson and Roben, and it is further said that his followers included Doji and Dokyo.