Khagan or Qagan was a titled used by Mongolic and Turkic peoples to denote the rank of emperor. It roughly translates to 'Khan of Khans', which is equivalent to the Persian Shahanshah (Shah of Shahs, that is, King of Kings).
The term Khagan referred to the leaders of the tribes of nomadic peoples in the Pardrayan steppes. It was used on both sides of the Shaum River, with the Arshaum and the Khamorth. A khagan who led the most powerful clan amongst the Khamorth was said to be the Royal Khagan, and his tribe the Royal Clan.
During the War Against the Yezda, the Lexovii chieftain Viridovix and the Greek physician Gorgidas, one fleeing the Videssian Emperor's wrath and the latter fleeing the death of his lover, rode with a Videssian embassy to the major Arshaum khagan in the Shaumkil in an effort to persuade him to join the fight against the Yezda. Along the way, they witnessed Avshar manipulate the outlaw Varatesh into becoming Royal Khagan and do his will. In the end, they took part in the battle against Varatesh and Avshar.