Arius (/əˈraɪəs, ˈɛəri-/; Koinē Greek: Ἄρειος, Áreios; 250 or 256–336) was a Cyrenaic presbyter, ascetic, and priest best known for the heretical doctrine of Arianism. His teachings about the nature of the Godhead in Christianity, which emphasized God the Father's uniqueness and Christ's subordination under the Father, and his opposition to what would become the dominant Christology, Homoousian Christology, made him a primary topic of the First Council of Nicaea convened by Emperor Constantine the Great in 325.