Wikipedia
Hzak
Hzak (Hza, Kzak) - the Cumans Khan, the head of the Cumans Of Don river (the Burchevichs), a son of the Beglyuk (Belyuk) Khan. In chronicles he is called Koza Burnovich. However, it's not excluding, that Kzak Belyukovich and Koza Burnovich are different persons.