The population of Estonian Orthodox Church of Moscow Patriarchate is 150,000.
The population of Estonian Apostolic Orthodox Church is 20,000.
Estonian Orthodox Church of Moscow Patriarchate was created in 1920.
The heads of the Orthodox church are called Patriarchs. There are seven patriarchates, lead by the Primate, Ecumenical Patriarch Bartholomew I of Constantinople.
Syriac Orthodox Church's population is 5,600,000.
The population of Orthodox Church in America is 1,000,000.
Japanese Orthodox Church's population is 30,000.
Romanian Orthodox Church's population is 18,806,428.
The population of Polish Orthodox Church is 600,000.
The population of Ethiopian Orthodox Tewahedo Church is 45,000,000.
The various 12 branches of The Orthodox Church have their own Patriarch that "governs" the jurisdiction of the Patriarch, yet The Ecumenical Patriarch is the head Patriarch who oversees all of the Patriarchates and The Orthodox Faithful across the Earth.
The head of the Orthodox Church is Jesus Christ. The spiritual leaders are the four Ancient Patriarchates (ie. Constantinople, Alexandria, Antioch, Jerusalem) followed by the leaders of the "Autocephalous" (self-governing) churches, such as Moscow, Greece, Serbia, etc. The Orthodox Church has no pope as the sole leader. The highest authority in the Orthodox Church is an Ecumenical Council (or Synod) that consists of the spiritual leaders (or their representatives) from the whole Orthodox world.
Until 1054, the year of the Great Schism, there were five patriarchates, or seats of authority, of the Church founded by Christ: Rome, Constantinople, Antioch, Alexandria, and Jerusalem. After the Schism, the Patriarch of Rome became the Pope of the, from that point on, Catholic Church. All the other Patriarchates continued as the Orthodox Christian Church. Constantinople was never Roman Catholic. The Greek Orthodox Christian Church in Constantinople/Istanbul is currently under attack by the Muslim Turkish government. The government will not allow an Orthodox Christian seminary to be built, and will not allow Orthodox priests to come from other countries. None of us know exactly what it was like back in 1054. edit: And the Orthodox Church does *not* recognize the Pope as anything but the head of the Catholic Church.