KHAGAN (Ḵāqān, “supreme ruler”), title of Xianbei (a leading nomadic group in northern China) origin that entered Persian during the first Turkish empire and has been used by medieval Muslim historians in reference to various rulers, including heads of Turkish federations, the emperor of China, etc.

The first records of the title khagan are in Chinese texts describing 3rd-century CE Xianbei tribes in Mongolia (Golden, 1992, pp. 70-71). By then, the Xianbei, most probably Proto-Mongolic in speech, had replaced the Xiongnu as the leading confederation in the steppe.  This confederation is regarded as a loose political association, less organized than the Xiongnu power.  Nevertheless, it is among one of the Xianbei tribes, the Qifu, that the title is first mentioned in 265 (Jinshu, 125.3113).  The old Xiongnu title of shanyu, with its century-old meaning of leader of the nomadic peoples, disappeared from the sources and is replaced in this sense by the title of khagan up to the Mongol period.  The etymology of the term is unclear, but it does not seem to be a Mongol, Turkish, or Iranian term (Golden, 1992, pp. 71-72).  It was soon in use among the various Xianbei tribes, and the various confederations tracing back their origins to the Xianbei, among them the Tuyuhun on the northeastern part of the Tibetan plateau and the Rouran (Juanjuan), who dominated Mongolia from the end of the 4th to the middle of the 5th century. It is with the flight of the Rouran after their defeat by the Turks, under their own name of Awar-Huns, that the title reached the West in the middle of the 6th century, transcribed in Byzantine texts as Χαγανοϛ (Menander, p. 50). Its earliest mention in Iranian texts seems to be in the Bugut inscription dedicated to the dead khagan Tatpar in 581 in Mongolia; it is written in Sogdian, in which the title is transcribed x’γ’n (ḵāqān).  The title of the wife of the khagan, the ḵātun, is regarded as Sogdian (x’ttwnh in the 595 Mongolküre inscription, from xwt’yn, wife of the lord; Clauson, p. 602).  In Iranian texts in Central Asia, the first mention of Khagan seems to be in the Bactrian documents, transcribed καγανο.  The earliest mention is dated 630 in document N, a peace agreement in a local context but with a politically Turkish titular (Sims-Williams, p. 74).  Theoretically, it would be possible that the title arrived sooner in Iranian-speaking Central Asia, since there was a short period of involvement of the Rouran there in the middle of the 5th century, as testified both by the Armenian and Chinese sources; the Rouran fought against the Kidarites and submitted to the Hephthalites before the rise of the latter to power, and conquered Khotan as well (Beishi, 3210) 

Actually, it was in the empires ruled by Turks that the title received a wider dissemination.  All the Turkish-speaking empires, from the unified ones centered in Mongolia (e.g., Uyghur Empire) to the various confederations or groups in Central Asia or north of the Caucasus (e.g., Türgesh, Khazars, etc.) made use of the title (see Clauson p. 611).  A special enthronement ritual is known both for the Turkish and the Khazar khagans, including ritual strangulation and shamanic ceremonies (Golden, 2007). 

The title soon became used for positions on various levels. The supreme khagan of an empire was marked by the adjunction of the Indic Maha (great) in front of the title to distinguish the bearer from all the subordinate khagans, a necessary feature in the Turkish political system. Each of these subordinate khagans, usually a brother of the supreme khagan, was in charge of a part of the empire, and there could be up to eight of them (Drompp).  For instance, the conqueror of Tiflis and ally to the Byzantine emperor Heraclius in the Caucasus in 627-28 was named in the Armenian and Byzantine sources the Viceroy Ziebel, while in the Chinese sources he is known as the Small Khagan Sipi (Xiao Ke-han Sipi; in Xin Tangshu, 215.6057; see la Vaissière, 2010, pp. 268-70). The supreme khagan, Tong Yabghu Khaqan, was his brother, reigning in Central Asia. The much older title Yabghu (Jabḡuya), known at least since the 2nd century BC, is quite often added to the title Khagan in the Iranian speaking regions of Central Asia (e.g., the Yabghu of 8th century Tokharestan, trace back their ancestry to Tong Yabghu Khagan).  

The Islamic texts inherited both a generic meaning of khagan as the supreme lord of the power of the North, sometimes extended to all of the powers outside of the Islamic realms to the North and the East (hence the depiction of a Chinese or a Tibetan khagan in both Muslim texts and pre-Islamic Turkish texts), and to a more specific reality, the many khagans encountered during the conquest of Central Asia.  Ebn al-Balḵi (p. 97) states that the khagan was one of the four kings of the world, with the Persian, Chinese, and Byzantine emperors, thus reflecting older pre-Islamic tradition as depicted in the Afrasiab painting of Samarkand, where the khagan might have been displayed on the main wall (la Vaissière, 2006).  When the Arabic armies arrived in Central Asia, not only did they have to fight against a major khagan, Sulu (d. 738), who founded the Türgesh khaghanate (704-56), but also here and there various small khagans holding only a fortress or leading a single tribe.  In ʿAbbasid Samarra, several high ranking Turks are called khagans or descendants of khagans, for instance Ḵāqān ʿOrṭuj, father of Fatḥ b. Ḵāqān, the companion of al-Motawakkel (r. 847-62); or Joff b. Yaltekin b. Furān b. Furi b. Ḵāqān (on their social background la Vaissière, 2007, pp. 180-81).  

In the 9th and 10th century, north of the frontier of Islamic Central Asia, the Qarluqs are described as a tribe with a khagan by Gardizi (p. 257).  In the 10th century, the Qarakhanids (see ILAK-KHANIDS), emerging from the Islamized Qarluqs or Yagma tribes, became par excellence the Ḵāqāni dynasty.  Later, in the Saljuk period, some local rulers bore the title in the Islamic world.  It is from such a ruler, the Šerwānšāh Manučehr, graced with the title Ḵāqān-e Kabir, that Ḵāqāni Šervāni (q.v.), the outstanding Persian poet of the 12th century, derived his poetic name (taḵalloṣ).  It is not clear when and where the title khan was created on the basis of khagan.  It cannot have been in a Turkish context (Clauson, p. 611), although khan is already in use in the 8th century Orkhon inscriptions. Maḥmud Kāšgari (ed. and tr. Dankoff, VII/2, p. 229) regarded the two words as synonymous.