Mark of Ephesus (born Manuel Eugenikos) was a hesychast theologian of the late Palaiologan period of the Byzantine Empire who became famous for his rejection of the Council of Ferrara-Florence (1438–1439). As a monk in Constantinople, Mark was a prolific hymnographer and a devoted Palamite. As a theologian and a scholar, he was instrumental in the preparations for the Council of Ferrara-Florence, and as Metropolitan of Ephesus and delegate for the Patriarch of Alexandria, he was one of the most important voices at the synod. After renouncing the Council as a lost cause, Mark became the leader of the Orthodox opposition to the Union of Florence, thus sealing his reputation as a defender of Eastern Orthodoxy and pillar of the Eastern Orthodox Church.