Ecumenical Patriarch

The Ecumenical Patriarch is the Patriarch of Constantinople. Today, Constantinople is called Istanbul. He is regarded to be the leader of the Eastern Orthodox Church. He has been generally known as the "Greek Patriarch of Constantinople". There is also an Armenian Patriarch of Constantinople (which is different). The older of the office is the Archbishop of Constantinople. The office should also not be taken for the Latin Patriarch of Constantinople, which no longer exists.
The current Ecumenical Patriarch is Bartholomew I
Orthodox Churches are autocephalous. This means there is a Patriarch for each Church, and there is usually one Church per country. For this reason, the Ecumenical patriarch is primus inter pares ("First among equals").