Yabghu

Yabghu (𐰖𐰉𐰍𐰆, ), also rendered as Jabgu, Djabgu or Yabgu, was a state office in the early Turkic states, roughly equivalent to viceroy. The title carried autonomy in different degrees, and its links with the central authority of Khagan varied from economical and political subordination to superficial political deference. The title had also been borne by Turkic princes in the upper Oxus region in post-Hephthalite times.

The position of Yabgu was traditionally given to the second highest member of a ruling clan (Ashina), with the first member being the Kagan himself. Frequently, Yabgu was a younger brother of the ruling Kagan, or a representative of the next generation, called Shad (blood prince). Mahmud Kashgari defined the title Yabgu as "position two steps below Kagan", listing heir apparent Shad a step above Yabgu.

As the Khaganate decentralized, the Yabgu gained more autonomous power within the suzerainty, and historical records name a number of independent states with "Yabgu" being the title of the supreme ruler. One prominent example was the Oguz Yabgu state in Middle Asia, which was formed after the fragmentation of the Second Türkic Kaganate in the 740s. Another prominent example was the Karluk Yabghu, the head of the Karluks which in the 766 occupied Suyab in the Jeti-su area, and eventually grew into a powerful Karakhanid state.

Etymology
There are at least several proposals regarding the origin of yabgu:
 * Yabghu might be a derivation from native Turkic root *yap- "to do, to carry out; to come nearer to help" and so might mean "the assistant (of the khagan)".
 * Others suggest that the word is a derivation of the early Turkic davgu; however, the d /ð/ to y /j/ sound change happened late (e.g. not before (561 - 618 CE)).
 * It is believed by some scholars to be of Kushan (Chinese: Guishuang  貴霜) political tradition, borrowed by the Göktürks from an Indo-European language, and preserved by the Hephtalites. For example, Harold Bailey reconstructs *yavuka ~ *yāvuka, which means "gatherer of troops" or "troop-leader" and is from base yau-, yū-, and yu- "to bring together", cognate with Avestan yavayeiti, yūta and Old Indian yú- "companion" and yūthá- "group";
 * Others, such as Sims-Williams, considered that the word yabgu in Turkic languages had been borrowed from Old Chinese i̯əp-g’u > xīhóu, rendered in Chinese characters as 翕侯 or 翖侯 Conversely, Friedrich Hirth suggested that yabgu was transcribed literary Chinese, with regard to Kushan and Turkic contexts, as *xiap-g’u > xīhóu.  It was equivalent to the title yavugo found on Kushan  coins from Kabul, and the yabgu on ancient Turkic monuments.  The second part of this compound Chinese word, hou ("g’u"), referred to the second-ranking of five hereditary noble ranks. Chinese sources do not make clear whether the title was a descriptive term used only in reference to foreign leaders, or whether it indicated an ally or subject of a Chinese empire;
 * Another theory postulates a Sogdian origin for both titles, "Yabgu" and "Shad". The rulers of some Sogdian principalities are known to have title "Ikhshid";
 * Yury Zuev considered Yabgu to be a "true Tocharian" title.