Yabaku is a fairly enigmatic tribe out of ten prominent Türkic tribes enumerated by Mahmut Kashgari (11th century) in the list describing the location of the Türkic polities from the borders of the Eastern Roman Empire to the borders of China in the following sequence: Yabāqu can be related etymologically to Turkic yapağu, "originally denoting 'matted hair or wool' and then an animal characterized by this, e.g. a 'colt.'
[4] According to Kashgari, Yabaku chief Böke Budrach led a pagan coalition from Western Siberia or further east across the Irtysh river to wars against Islamic Kara-khanid khanate (comprising modern Western and Eastern Turkestan); Karakhanid heroic epics also mentioned these invasions, which Karakhanids thwarted successfully.
Kashgari cited a witness, who related that Ghazi Arslan Tegin defeated the Yabaku-led coalition and captured Budrach.
[6][7] Golden proposes that the authority of the Yabaqu, as the coalition's leading tribe, extended also to their allies the Basmils and the Qays.
Noting that Kashgari glossed Budrach's epithet Böke as "large dragon (ṯu'bān 'aẓim)"[8] - which might also mean "great snake", Golden further identifies Budrach's coalition, as "People of the Chieftain named Snake/Dragon", with the "Snake People" who had driven out the "Pale Ones" (xartêš), causing the "Pale Ones" to dislodge the Oghuz Turks, who in turn expelled the Pechenegs, in the account given by Matthew of Edessa.