Кага́н ....
Впервые засвидетельствован в китайских источниках применительно к центрально-азиатскому племени сяньби (III век).
Origin
The title was first seen in a speech between 283 and 289, when the Xianbei chief Murong Tuyuhun tried to escape from his younger stepbrother Murong Hui, and began his route from Liaodong to the areas of Ordos Desert. In the speech one of the Murong's general named Yinalou addressed him as kehan (可寒, later as 可汗), some sources suggests that Tuyuhun might also have used the title after settling at Koko Nor (Qinghai) in the 3rd century.[3]
The Rourans were the first people who used the titles Khagan and Khan for their emperors, replacing the Chanyu of the Xiongnu, whom Grousset and others assume to be Turkic.[4] However, many scholars believe the Rouran were proto-Mongols.[5][6][7]
The Avars, who may have included Rouran elements after the Göktürks crushed the Rouran who ruled Mongolia, also used this title. The Avars invaded Europe, and for over a century ruled the Carpathian region. Westerners Latinized the title "Khagan" into "Gaganus" or Cagan et Iugurro principibus Hunorum.