Mark of Ephesus was a 15th-century Byzantine monk, theologian, and archbishop who lived in Constantinople. A dedicated follower of Gregory Palamas, he was a prolific hymnographer and scholar. He is most famous for his role at the Council of Ferrara–Florence, where he initially supported the union but eventually became the primary leader of the Orthodox opposition. By rejecting the council's agreement due to its inconsistency with established dogmas, he earned a reputation as a defender of the faith. He is venerated as a saint in both Catholic and Orthodox traditions.