KHAGAN, alternatively spelled Chagan, Qaqan etc, is a title of royal or imperial rank in Mongolian and Turkic languages. In modern Mongolian it became Khaan.
As its etymological meaning 'Khan of Khans' indicates, it ranks above all other Khans in an empire or realm - as the sovereign, in the manner of a King of Kings (see that article for parallels).
The common western rendering as Great Khan, notably in the case of Dhengiz Khan's dynasty, is technically not quite correct, but established rather well by long-standing convention and reasonably clear in suggesting paramount status.
The first known use would be by the nomadic Juan Juan confederacy (4th-6th century AD) on China's northern border
Khan (sometimes spelled as xan, han) is a title meaning ruler in Mongolian. ... For the movie of this name, see King of Kings (movie). ... KHAGAN, alternatively spelled Chagan, Qaqan etc, is a title of royal or imperial rank in Mongolian and Turkic languages. ... Juan Juan ( wg), Ruanruan ( py), Ru Ru (py) or Rouran 柔然 (py) was the name of a confederacy of nomadic tribes on the northern borders of China proper from late 4th century until late 6th century. ...
It is clear that khan Kubrat was a man who had acquired in Byzantium great knowledge about the structure and functioning of the state machinery and who, without doubt, tried to establish a perfectly workable administration in his new state after bringing it in conformity with the local conditions and tradition.
The decisive support of khan Kubrat to Martina, widow of his friend, the emperor of the East Roman Empire Heraclius, and her son Heraclonas, is described in the Chronicle of John, Bishop of Nikiou.
The developments that followed khan Kubrat's death indicate that part of the Bulgarians, or rather their political leaders, had insisted on the state being defended only within its existing territories (khan Kubrat had evidently belonged to that group, and his supreme power and prestige had those who disagreed with his policy refrain from action).
Khan was also probably the title used by early Bulgar rulers, but is not attested in any inscriptions referring to them- the only similar title found so far, Kanasubigi, was used by only three of the Bulgarian rulers, namely Krum, Omurtag and Malamir, which were grandfather, son and a grandson, after them the title disappears.
Khan was the title of the rulers of various break-away states later reintegrated in Iran, e.g.
The title Khan of Khans was among numerous titles used by the Sultans of the Ottoman empire as well as the rulers of the Golden Horde and its descendant states.