The Christian theologian St. Athanasius (ca. 296-373) was bishop of Alexandria, in Egypt. He was the most eminent Church leader opposing Arianism on the basis of the creed adopted by the Council of Nicaea in 325.

Athanasius was probably born at Alexandria. By his early 20s he was both a deacon in the Church and secretary to Alexander, Bishop of Alexandria. In 325 he accompanied Alexander to the Council of Nicaea, a meeting of Christian bishops that has become renowned as the first ecumenical council of the Church. The council was summoned by Emperor Constantine to deal with a controversy that had first arisen between Bishop Alexander and Arius, a presbyter at Alexandria. By 325 the dispute had broadened so as to appear to pose a threat to the unity of the Church in the eastern part of the Roman Empire. The controversy concerned the compatibility of belief in the oneness...