Aetius, surnamed the Atheist, from his supposed denial of the God of revelation, an oriental heresiarch, born in Antioch, died in Constantinople, A. D. 367. In early life he was successively the slave of a vine-dresser's wife, a travelling tinker or a goldsmith, and a quack doctor. He then studied medicine and theology at Antioch, and became prominent as a disputant. His theories (the chief of which were the Anomcean doctrines that the Son is of a nature unlike and inferior to that of the Father, and that the Holy Spirit is but a creature made by the Father and Son before all other creatures) incensed the Arians, and he was thrice compelled to seek safety in flight; but at length he was ordained deacon by Leontius, bishop of Antioch. He now developed, in connection with Eunomius, his pupil and amanuensis, a new schism known as the Aetian or Eunomian heresy, and made many disciples. He was condemned by the council of Seleucia in 359, and banished by Con-stantius to Amblada, in Pisidia. After the death of Constantius he was recalled to Constantinople by Julian, and made a bishop.

He adopted every means of spreading his heresy, but, having by his intrigues and immorality alienated all his friends, died unpitied by any but Eunomius, who buried him.