Athanasius of Alexandria (Greek: Ἀθανάσιος, Athanásios) (b. ca. 296-298 – d. 2 May 373), also referred to as St. Athanasius the Great, St. Athanasius I of Alexandria, St Athanasius the Confessor and (primarily in the Coptic Orthodox Church) St Athanasius the Apostolic, was the 20th bishop of Alexandria. His episcopate lasted 45 years (c. 8 June 328 - 2 May 373), of which over 17 were spent in five exiles ordered by four different Roman emperors. He is considered to be a renowned Christian theologian, a Church Father, the chief defender of Trinitarianism against Arianism, and a noted Egyptian leader of the fourth century.

He is remembered for his role in the conflict with Arius and Arianism. In 325, at the age of 27, Athanasius had a leading role against the Arians in the First Council of Nicaea. At the time, he was a deacon and personal secretary of the 19th Bishop of Alexandria, Alexander. Nicaea was convoked by Constantine I in May–August 325 to address the Arian position that Jesus of Nazareth is of a distinct substance from the Father.