If your talking about the Byzantine Emporor, he was never head of the church, though, like in many countries, often got involved in church politics (I know the Pope of Rome often stuck his nose into Catholic monarchies). In Constantinople & other places, since Orthodoxy was the state religion, it was often involved in politics, and the emporor, ruler, whatever would also get involved in religion. It was common for Orthodox bishops & kings to be brothers or relatives. But to say the monarchs were the heads of the church is just uneducated. Only 2 people that I can think of are both heads of state & heads of churches (there might be others), Queen Elizabeth II & Pope John Paul II.