Quote Originally Posted by Baba Ga'on
He wasn't. The emperor in Constantinople was far more Greek than he ever was Roman.

Also, "tsar" does not mean emperor. It is a title that a Bulgarian ruler managed to wean off the Byzantine emperor after he inflicted a crushing defeat on him. This title was "Caesar," a position of subservience to the emperor. It was more akin to king than it was to emperor.
Actually Caesar (and it's slavic derviatives) does mean emperor. Emperor had two levels to the Romans. The Augustus was the senior emperor, the Caesar the junior emperor. So if the Serbian ruler took the title Tsar. It mean't he was claiming a position akin to junior Roman emperor.