Arius (urī'us, âr'ē–) [key], c.256–336, Libyan theologian, founder of the Arian heresy. A parish priest in Alexandria, he advanced the doctrine famous as Arianism and was excommunicated locally (321). He was declared orthodox in Asia Minor, where he had fled (323), but he was anathematized by the Council of Nicaea (see Nicaea, First Council of) and banished by Roman Emperor Constantine (325). But in the reaction after Nicaea, he came into imperial favor. The emperor had ordered the Athanasians at Alexandria to receive him at communion when he suddenly died.
