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He appears only in the account of the Byzantine court historians Kedrenos and John Skylitzes, who place him at Kerch and calls him "khagan" (the title of the Khazar emperors). Kedrenos states that he was captured by the expeditionary force but does not relate his ultimate fate. Inscriptions and other references exist referring to a Tzul or Tsal clan in Crimea during this period; presumably he was a member although the relationship of that family to the original ruling dynasty of Khazaria is unknown. Almost nothing else about him, including the extent of his holdings, is known.
Despite the fact that earlier writers maintained that the Khazar khagan was required to adhere to Judaism, Georgius is a Christian name. Whether Georgius Tzul was himself a Christian, a Jew or Shamanist with an unusual Greek name, or whether the name is merely a Byzantine attempt to transliterate a Turkic or Hebrew name, is unknown.
- Kevin Alan Brook. The Jews of Khazaria. 2nd ed. Rowman & Littlefield Publishers, Inc, 2006.