Dioscorus I, also known as Dioscorus the Great, was the pope of Alexandria and patriarch of the See of St. Mark who was deposed by the Council of Chalcedon in 451. He was recognized as patriarch by the Coptic Church until his death. He died in Gangra, Paphlagonia, in September 454. He is venerated as a saint by the Coptic and other Oriental Orthodox Churches.

The Council of Chalcedon was the fourth ecumenical council of the Christian Church. It was convoked by the Roman emperor Marcian. The council convened in the city of Chalcedon, Bithynia from 8 October to 1 November 451. The council was attended by over 520 bishops or their representatives, making it the largest and best-documented of the first seven ecumenical councils. The principal purpose of the council was to re-assert the teachings of the ecumenical Council of Ephesus against the teachings of Eutyches and Nestorius. Such doctrines viewed Christ's divine and human natures as separate (Nestorianism) or viewed Christ as solely divine (monophysitism).