Omeljan Pritsak speculated that a Khazar khagan named Khan-Tuvan Dyggvi, exiled after losing a civil war, settled with his followers in the Norse-Slavic settlement of Rostov, married into the local Scandinavian nobility, and fathered the dynasty of the Rus' khagans [REF].
Most historians agree that the title "khagan" was borrowed by the Rus from the Khazars, but there is considerable dispute over the circumstances of this borrowing.