what was the keader of eastern orthodox called

The leader of the Eastern Orthodox Church is usually called the Ecumenical Patriarch of Constantinople, and the current one is Bartholomew I. In many sources, he is also described as the spiritual leader or “first among equals” among Orthodox bishops.

A common simple answer is:

• Ecumenical Patriarch
• More specifically: Patriarch of Constantinople
• Current holder: Bartholomew I

If you want, I can also explain how that role differs from the Pope.