In Byzantium, the concept of the kingdom was not based on the Western feudal patterns we are familiar with today through movies and fairytales, but on ancient Roman models based on the election of the autocrat by the people, the Senate and the army.
In simpler terms, when we talk about the Roman Emperor in Byzantium, we should not imagine an absolute monarch who inherited the throne because he was simply the son of the previous monarch. The position of Byzantine autocrat was essentially another one office in the Byzantine state hierarchy.
Without the approval of the people of Constantinople, the Byzantine army and Senate, no one could become an Emperor. Whoever lost legitimacy as an Emperor was automatically considered a hated tyrant and had to be replaced.
Voting did not exist then, so usually the only way to replace was through popular uprisings, war, murder, cutting off a nose or blinding. For that reason, every new Byzantine emperor would distribute coins and gifts to the people, army and Synod in order to gain their acceptance.
Only in the last centuries of Byzantium did the concept of a Byzantine emperor begin to slowly blend with the Western way of thinking most people envision today.