Giku (date of birth and death unknown) was a Zen-sect priest from Tang China in the early Heian period.
He learned under 海昌院斉安国師 in Hang Zhou, China. When Empress Dowager TACHIBANA no Kachiko invited a Zen sect priest from Tang China by sending Egaku as the messenger in 835, Giku came to Japan due to 斉安's recommendation. At first Giku lived in To-ji Saiin (the western part of To-ji Temple) and then moved to Danrin-ji Temple, which was established by Kachiko, becoming the founder of the temple. It is said that a lot of people visited him for Buddhism, but the Zen sect itself didn't become popular and Giku returned to Tang after a few years. It is said that when Egaku revisited Tang China, he engraved Giku's accomplishments on a monument, sent it to Japan, and built it beside Rajomon Gate in Kyoto.