Li Keyong
After Li Keyong resubmitted to Tang authority and was made the military governor ("Jiedushi") of Yanmen Circuit ( or "Yànmén Dào") around present-day Datong in 882, he made Gai Yu a base supervisor as well as the prefect of Lan Prefecture (嵐州, in modern Lüliang, Shanxi). After Li Keyong was later made the military governor of Hedong Circuit (河東, headquartered in modern Taiyuan, Shanxi), Gai continued as a base supervisor. It was said that Li Keyong consulted him on all important matters and listened to his suggestions, and that he accompanied Li Keyong on all campaigns.