Khazar kingship was divided between the Khagan and the Bek or Khagan Bek. Contemporary Arab historians related that the Khagan was purely a spiritual ruler or figurehead with limited powers, while the Bek was responsible for administration and military affairs.
In the Khazar Correspondence, King Joseph identifies himself as the ruler of the Khazars and makes no reference to a colleague. It has been disputed whether Joseph was a Khagan or a Bek; his description of his military campaigns make the latter probable. A third option is that by the time of the Correspondence (c. 950–960) the Khazars had merged the two positions into a single ruler, or that the Beks had somehow supplanted the Khagans or vice versa.
Some sources refer to the Khazar Bek as ishad (a Göktürk military rank) or Malik (Arabic for "king", also used as a high rank). He was theoretically the subordinate of the Khagan but in reality controlled the military and civil government for the Khazar khaganate.
- Kevin Alan Brook. The Jews of Khazaria. 3rd ed. Rowman & Littlefield Publishers, 2018.
- Douglas M. Dunlop. The History of the Jewish Khazars, Princeton, N.J.: Princeton University Press, 1954.
- Peter B. Golden. Khazar Studies: An Historico-Philological Inquiry into the Origins of the Khazars. Budapest: Akadémiai Kiadó, 1980.
- Norman Golb and Omeljan Pritsak, Khazarian Hebrew Documents of the Tenth Century. Ithaca: Cornell University Press, 1982.