By this I mean that from the surviving records we have, they had a fairly sophisticated level of civilization. We know that they were able to keep the Byzantines, Cossacks, and Golden Horde back enough to get breathing room, and could project enough power to have favorable treaties at times. But we know very little about them.
Most people only remember that opening line: "Presently, Oleg the Wise makes ready to avenge the reasonless Khazars".
The rest of the legend has nothing to do with Khazars as such, but the ongoing confrontation with that tribe forms the background of the narrative. Prince Oleg meets a fortune teller (both Oleg and the fortune teller are pagans). Oleg asks to know his fate, and the old man tells him that he will be kept safe through all battles but he will "accept death from his horse".
Oleg laughs, but still orders his horse, whom he considers his best friend, to be retired. The horse is given best care, richest pastures, cleanest water, etc.
Many years pass and once, while enjoying a princely feast, Oleg remembers the horse of his yesteryear. He is told that the horse had died. Oleg curses scornfully at the memory of the fortune teller and, being a sentimental sort, Oleg wishes to see the bones of the horse. He is lead to the skeleton and wistfully he lifts up the skull. A snake, that had curled up in the skull slithers onto his glove, bites the hand, and Oleg drops dead.
I wonder if that can be added to the Mystery of the Jews.