The Emperor
The Ecumenical Patriarch (in Constantinople).
It was the Orthodox Church, or The Eastern Orthodox Church.
Yes, the Eastern Orthodox Church has deacons, priests and bishops.
Pope Francis is the supreme leader of the Catholic Church.
Constantinople was the capital of the Eastern Orthodox Church.
The emperor chose the patriarch of Constantinople, leading the Church official in the Byzantine Empire.The emperor became an autocrat and the head of the church as well as the state.
The highest christian official is the pope. The pope represents God on Earth. He has a special gift that god gave him. He can not make a mistake when saying the word of god.
Back in the days of Constantinople, the Orthodox Church was highly involved in government and politics. Even though there was separation of Church and State, the Church exercised considerable influence in the government of Constantinople.
The catholic church was never moved to constantinople, emperor constatine kept the church in Rome but moved the capitol to Constantinople. The SPRQ's belief of the church for salvation and emotional comfort kept the eastern empire alive for as long as it did, though it ultimately fell.
It was and is in Constantinople (Istanbul).
The Patriarch is the authoritative figure for The Greek Orthodox Church.
The Eastern Orthodox Church in Constantinople is called the Ecumenical Patriarchate, or is sometimes called the See of St Andrew (because it was founded by St Andrew).