It now has many equivalent meanings such as commander, leader, or ruler. Presently Khans exist mostly in South Asia, Central Asia, Pakistan, Afghanistan, and Iran. The female alternatives are Khatun and Khanum. Various Mongolic and Turkic peoples from Central Asia had given the title new prominence after the Mongol invasion and later brought the title "Khan" into Afghanistan and Northern India, which later was adopted by locals in the country as a name. Khagan is rendered as Khan of Khans and was the title of Genghis Khan and the other Khagans (his direct male descendants).
Originally khans only headed relatively minor tribal entities, generally in or near the vast Eurasian steppe, the scene of an almost endless procession of nomadic people riding out into the history of the neighbouring sedentary regions, mainly Europe and the Far East.
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, Rome and Byzantium.
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 - archontеs, 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, sometimes credited for having defeated the Arab invaders, thus "saving Europe"; Khan Krum, "the Terrible". "Khan" was the official title of the ruler until 864 CE, when Kniaz Boris (known also as Tsar Boris I) adopted the Eastern Orthodox faith.
The title Khan became unprecedently prominent when the tribal Mongol Temüjin proved himself a military genius by creating the Mongol empire, the greatest land empire the world ever saw, which he ruled as Genghis Khan. His title was khagan 'Khan of Khans', see below, but is often 'shortened' 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').
After Genghis' death, the empire would soon start a process of gradual disintegration, with his successors initially preserving the title "khan". Soon the Mongol element waned nearly everywhere, except in desolate regions like its native Outer Mongolia (even in China's 'Inner Mongolia') by sedentary people, and mainly Turkic, nomadic tribes that entered the scene rather like the Mongols had done before, conquering on horseback, to be in turn either sedentarized or overrun. Still, Genghis' prestige was such that a claim to descent from him was as prized as would be descent from Caesar in the West.
Ming Dynasty Chinese Emperors were also known as Khans by Mongols and Jurchens.
The title Khan was also used to designate the rulers of the Jurchens, who, later when known as the Manchus, founded the Qing dynasty of China. The Mongolian title of the Qing emperors, Bogd Khan, would later be used by the eighth Jebtsundamba Khutuktu after Mongolia's declaration of independence in 1911.
Once more, there would be numerous khanates in the steppe in and around Central Asia, often more of a people than a territorial state, e.g.:
While most Afghan principalities were styled emirate, there was a khanate of ethnic Uzbeks in Badakhshan since 1697.
Khan was the title of the rulers of various break-away states later reintegrated in Iran, e.g. 1747 - 1808 Khanate of Ardabil (in northwestern Iran east of Sarab and west of the southwest corner of the Caspian Sea), 1747 - 1813 Khanate of Khoy (northwestern Iran, north of Lake Urmia, between Tabriz and Lake Van), 1747 - 1829 Khanate of Maku (in extreme northwestern Iran, northwest of Khoy, and 60 miles south of Yerevan, Armenia), 1747 - 1790s Khanate of Sarab (northwestern Iran east of Tabrizlol), 1747 - c.1800 Khanate of Tabriz (capital of Iranian Azerbeidjan).
There were various small khanates in and near Transcaucasia. In present Armenia, there was a khanate of Erivan (sole incumbent 1807 - 1827 Hosein Quli Khan Qajar). Diverse khanates existed in Azerbaijan, including Baku (present capital), Ganja, Jawad, Quba (Kuba), Salyan, Shakki (Sheki, ruler style Bashchi since 1743) and Shirvan=Shamakha (1748 - 1786 temporarily split into Khoja Shamakha and Yeni Shamakha), Talysh (1747-1814); Nakhichevan and (Nagorno) Karabakh.
As hinted above, the title Khan was also common in some of the polities of the various - generally Islamic - peoples in the territories of the Mongol Golden Horde and its successor states, which, like the Mongols in general, were commonly called Ta(r)tars by Europeans and Russians, and were all eventually subdued by Muscovia which became the Russian Empire. The most important of these states were:
Examples of other, humbler Tatar khanate dynasties made vassals of Muscovy/ Russia are:
Further east, in imperial China's western Turkestan flank:
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. The title Khan was also used in the Seljuk Turk dynasties of the near-east to designate a head of multiple tribes, clans or nations, who was below an Atabeg in rank. Jurchen and Manchu rulers also used the title Khan (Han in Manchu); for example, Nurhaci was called Genggiyen Han. Rulers of the Göktürks, Avars and Khazars used the higher title Kaghan, as rulers of distinct nations.
The titles Khan (the lowest commonly awarded) and Khan Bahadur (Bahadur from Turkish baatar 'brave, hero'; but in India meaning simply 'one class higher') were also bestowed in feudal India by the Great mughal (whose protocol was largely Persian-inspired) upon Muslims and Parsis, and later by the British Raj, as an honor akin to the ranks of nobility, often for loyalty to the crown. Khan Sahib was another title of honour, one degree higher than Khan, conferred on Muslims and Parsis; again like Khan Bahadur, it was also awarded with a decoration during British rule.
In the major Indian Muslim state of Hyderabad, Khan was the lowest of the aristocratic titles bestowed by the ruling Nizam upon Muslim retainers, ranking under Khan Bahadur, Nawab (homonymous with a high Muslim ruler's title), Jang, Daula, Mulk, Umara, Jah. The equivalent for the courts Hindu retainers was Rai.
It seems unclear whether the series of titles known from the Bengal sultanate, including Khan, Khan ul Muazzam, Khan-ul-Azam, Khan-ul-Azam-ul-Muazzam etc. and Khaqan, Khaqan-ul-Muazzam, Khaqan-ul-Azam, Khaqan-ul-Azam-ul-Muazzam etc., are merely honorific or perhaps relate to a military hierarchy.
See jirga for local mediators called Khan.
Khan and its female forms occur in many personal names, generally without any nobiliary of political relevance (although it remains a common part of noble names as well). Notably on the Indian subcontinent it has become a part of many South Asian Muslim names, especially when Pashtun descent is claimed.
During the Russian Civil War following the Bolshevik takeover of 1917, White general Roman Ungern von Sternberg, who, admittedly was trying to reconstitute the empire of Genghis Khan, was often styled as "Ungern Khan" between 1919 and his death in 1921.