What is khagan?

Some articles on khagan, khagans:

Third Perso-Turkic War - Background
... to the steppes his emissary, named Andrew, who promised to the Khagan some "staggering riches" in return for military aid ... The khagan, on his part, was anxious to secure the Chinese-Byzantine trade along the Silk Route, which had been disrupted by the Persians in the aftermath of the Second Perso-Turkic War ... Persian Transcaucasia and delivered the Khagan's message to the Byzantine camp in Anatolia ...
List Of Ukrainian Rulers - Migration Period (c. 200 – C. 800) - Hunnic Rulers
430) Rugila aka Ruga (Rua, Roila), Yabgu (prince), then Khagan (432–434) Mundzuk aka Aybat, Yabgu (390–434), Khagan (434) Bleda, Khagan and ruler of Eastern Huns (Ak Bulgar) (434–445) Attila the Hun, Yabgu of ...
Rus' Khaganate - Origin
... Omeljan Pritsak speculated that a Khazar khagan named Khan-Tuvan Dyggvi, exiled after losing a civil war, settled with his followers in the Norse-Slavic settlement of Rostov, married ... as untenable speculation, and no record of any Khazar khagan fleeing to find refuge among the Rus' exists in contemporaneous sources ... The genealogical connection between the 9th century Khagans of Rus' and the later Rurikid rulers, if any, is unknown at this time ...
Tian Kehan
... T'ien K'ehan) also translated as Heavenly Khagan, Celestial Khagan or Tengri Khagan, was a title addressed to Emperor Taizong of Tang by various Turkic nomads ... The title Tengri Khagan also used to refer another two Turkic ruler, both known as the Dengli Khagan to the Chinese, during the Second Eastern Turkic Khaganate (r ...
Rus' Khaganate - Government
... Ibn Fadlan described the Rus' ruler (like the Khazar khagan), as having little real authority ... right up to the throne." Ibn Rustah, on the other hand, reported that the khagan was the ultimate authority in settling disputes between his subjects ... one of the disputants disagreed with the khagan's ruling, the dispute was then resolved in a battle, which took place "in the presence of the contestants' kin who stand with swords ...