Arianism is the theological teaching attributed to Arius (ca.

250–336), a Christian presbyter in Alexandria, Egypt, concerning the relationship of the persons of the Trinity ('God the Father', 'God the Son', and 'God the Holy Spirit') and the precise nature of the Son of God as being a subordinate entity to God the Father.

Deemed a heretic by the First Council of Nicaea of 325, Arius is later exonerated in 335 at the First Synod of Tyre, and then, after his death, pronounced a heretic again at the First Council of Constantinople of 381.

The Roman Emperors Constantius II (337–361) and Valens (364–378) are Arians or Semi-Arians.The concept of Christ is that the Son of God did not always exist, but was created by—and is therefore distinct from—God the Father.

This belief is grounded in the Gospel of John passage “You heard me say, ‘I am going away and I am coming back to you.’ If you loved me, you would be glad that I am going to the Father, for the Father is greater than I."

(verse 14:28)Arianism is defined as those teachings attributed to Arius which are in opposition to mainstream Trinitarian Christological doctrine, as determined by the first two Ecumenical Councils and currently maintained by the Roman Catholic Church, the Eastern Orthodox Churches, and most Reformation Protestant Churches.

"Arianism" is also often used to refer to other nontrinitarian theological systems of the 4th century, which regard Jesus Christ—the Son of God, the Logos—as either a created being (as in Arianism proper and Anomoeanism), or as neither uncreated nor created in the sense other beings are created (as in Semi-Arianism).