Sabellius, fl. 215, Christian priest and theologian, b. probably Libya or Egypt. He went to Rome, became the leader of those who accepted the doctrine of modalistic monarchianism, and was excommunicated by Pope St. Calixtus I in 220. Opposing the orthodox teaching of "essential Trinity," Sabellius advanced the doctrine of the "economic Trinity." God, he held, was one indivisible substance, but with three fundamental activities, or modes, appearing successively as the Father (the creator and lawgiver), as the Son (the redeemer), and as the Holy Spirit (the maker of life and the divine presence within men). The term Sabellianism later was used to include all sorts of speculative ideas that had become attached to the original ideas of Sabellius and his followers. In the East, all monarchians came to be labeled Sabellians.