Christian theologian, a native of Alexandria, and a deacon of the Church; took a prominent part against Arius in the Council at Nice, and was his most uncompromising antagonist; was chosen bishop of Alexandria; driven forth again and again from his bishopric under persecution of the Arians; retired into the Thebaïd for a time; spent the last 10 years of his life as bishop at Alexandria, where he died; his works consist of treatises and orations bearing on the Arian controversy, and in vindication of the doctrine of the Trinity viewed in the most absolute sense (296-373).