What is "ketuyu"

Ketuyu (可突于 died 734) was a Khitan military chief, notable for his Ketuyu rebellion. Despite the presence of a King, he de facto controlled Khitan politics. His power made the Khitan King jealous, and he then defended himself by making a coup in 720, against King Suogu. By this action, he incurred Tang China opposition and they sent military campaigns against him, which he defeated several times. He was eventually crushed by repeated Chinese campaigns, and was murdered together with King Qulie by his subordinate Li Guozhe.