Rurik a Doge?

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I was just wondering if anyone else has noticed or has Rurik the founder of the Kievan Rus Dynasty the title Doge which is an Italian title rather than rus, is son is also one and to make it more confusing his grandsons Yaropolk is an Jarl , Vladimir a doge and Oleg a Duke, is this some kind of cultural, religious fault??

Traditionally Yaropolk is supposed to be a prince and the anothers Grand Princes, if were super authentic then its actually Velikiy knyaz

 

[Slaxl]

I made a baron in Cornwall a Doge, he was mayor and I liked the cut of his jib so I thought I'd make him count, so gave him the county, little did I know this made him Lord Mayor. He then claimed the Duchy which made him Doge. Actually I'm rather hazy on the details, I remember the first two parts happening, but I'm speculating on the third, as I wasn't watching.