"Khan" also occurs as a title in the Xianbei confederation for their chief between 283 and 289. The Rourans may have been the first people who used the titles khagan and khan for their emperors. However, Alexander Vovin (2007) believes that the term qaγan originated among the Yeniseian-speaking Xiongnu people, and then diffused across language families. Subsequently, the Göktürks adopted the title and brought it to the rest of Asia. In the middle of the sixth century the Iranians knew of a "Kagan – King of the Turks".
Various Mongolic and Turkic peoples from Central Asia gave the title new prominence after period of the Mongol Empire (1206–1368) in the Old World and later brought the title "khan" into Northern Asia, where locals later adopted it. Khagan is rendered as Khan of Khans. It was the title of Chinese Emperor Emperor Taizong of Tang (Heavenly Khagan, reigned 626 to 649), and also the title of Genghis Khan and of the persons selected to rule the Mongol Empire. For instance Möngke Khan (reigned 1251-1259) and Ogedei Khan (reigned 1229-1241) would be "Khagans" but not Chagatai Khan, who was not proclaimed ruler of the Mongol Empire by the kurultai.
Originally khans headed only relatively minor tribal entities, generally in or near the vast Mongolian and North Chinese steppe, the scene of an almost endless procession of nomadic people riding out into the history of the neighbouring sedentary regions. Some managed to establish principalities of some importance for a while, as their military might repeatedly proved a serious threat to such empires as China and kingdoms in Central Asia.
One of the earliest notable examples of such principalities in Europe was Danube Bulgaria (presumably also Old Great Bulgaria), ruled by a khan or a kan at least from the 7th to the 9th century. It should be noted that the title "khan" is not attested directly in inscriptions and texts referring to Bulgar rulers – the only similar title found so far, Kanasubigi, has been found solely in the inscriptions of three consecutive Bulgarian rulers, namely Krum, Omurtag and Malamir (a grandfather, son and grandson). Starting from the compound, non-ruler titles that were attested among Bulgarian noble class such as kavkhan (vicekhan), tarkhan, and boritarkhan, scholars derive the title khan or kan for the early Bulgarian leader – if there was a vicekhan (kavkhan) there was probably a "full" khan, too. Compare also the rendition of the name of early Bulgarian ruler Pagan as Καμπαγάνος (Kampaganos), likely resulting from a misinterpretation of "Kan Pagan", in Patriarch Nicephorus's so-called Breviarium In general, however, the inscriptions as well as other sources designate the supreme ruler of Danube Bulgaria with titles that exist in the language in which they are written – archontes, meaning 'commander or magistrate' in Greek, and knyaze, meaning "duke" or "prince" in Slavic. Among the best known Bulgar khans were: Khan Kubrat, founder of Great Bulgaria; Khan Asparukh, founder of Danubian Bulgaria (today's Bulgaria); Khan Tervel, who defeated the Arab invaders in 718 Siege of Constantinople (718), thus stopped the Arab invasion in Southeast Europe; Khan Krum, "the Terrible". "Khan" was the official title of the ruler until 864 AD, when Kniaz Boris (known also as Tsar Boris I) adopted the Eastern Orthodox faith.
The title Khan became unprecedently prominent when the Mongol Temüjin created the Mongol empire, the greatest land empire the world has ever seen, which he ruled as Genghis Khan. His title was khagan, or "Khan of Khans", but has often been abbreviated to Khan (rather like the Persian Shahanshah -also meaning "King of Kings"- is usually called Shah, equally incorrect, in most Western languages) or described as "Great Khan" (like the Ottoman Padishah being called "Great Sultan"). The great leader was regarded as a khan in the middle east and Asia. Ming Dynasty Chinese Emperors also used the term Xan to denote brave warriors and rulers. The title Khan was used to designate the greatest rulers of the Jurchens, who, later when known as the Manchus, founded the Manchu Qing dynasty.