Ikuu

...Abstaining from meat and grains and eating only nuts and grass is called mokujiki, and a high priest who continues this practice is called mokujiki monk. Ogo (Mokujiki Ogo) of the Azuchi-Momoyama period, who contributed to the restoration of Mount Koya, is widely known as mokujiki monk, but there are many high priests who were revered as mokujiki monks, such as Ikuu, who continued ascetic practices at Katsuo-ji Temple in Settsu in the early Edo period and was known as a miraculous monk, Yoa, who became the founder of the restoration of Ansho-in Temple in Gojozaka, Kyoto in the middle period, Yoshitaka, known as the founder of mokujiki temple in Yushima, Edo, and Gogyo (Mokujiki Gogyo Myoman), who carved unique Buddhist statues and contributed to educating the common people in the later period. Mokujiki was one of the ascetic practices, and it was said that by doing it one could purify the body and strengthen the mind, but there is no source of mokujiki in the sutras or rituals. ...

*Some of the terminology explanations that mention "Ikuu" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…肉類，五穀を食べず，木の実や草などを食料として修行することを木食といい，その修行を続ける高僧を木食上人といった。高野山の復興に尽くした安土桃山時代の応其（おうご）(木食応其)は，広く木食上人の名で知られるが，江戸時代前期には摂津の勝尾寺で苦行を続け霊験あらたかな僧として知られた以空（いくう），中期には京都五条坂の安祥院中興の祖となった養阿，江戸湯島の木食寺の開基として知られる義高，後期には特異な様式の仏像を彫刻して庶民教化に尽くした五行(木喰五行明満)があらわれるなど，木食上人として崇敬された高僧は少なくない。木食は苦修練行の一つで，それを行うことによって身を浄め，心を堅固にすることができるとされたが，経典や儀軌の中に木食の典拠は見いだせない。…

※「以空」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報