When and How in the History of Theology Did the Triune God Replace the Father as the Only True God?

A traditional view is that Christians have always believed that the one God is three Persons in one essence or being. Orthodox analytic theologian Beau Branson has recently argued that this is untrue, as earlier “fathers” taught that the one God just is the Father. He argues that this sensible Eastern view was misunderstood by Western sources, which is how the idea of the one God as tripersonal entered into mainstream Christian theologies. While I agree with Branson that in about the first three Christian centuries the teaching was that the one God just is the Father, I argue that his account about when and how the idea of a triune God comes in is mistaken, because we can see this new idea of a tripersonal God appearing in both Eastern and Western sources around the time of the council at Constantinople in 381, the surviving statement of which is the earliest “official” creed which assumes and implies that the one God is the Trinity, the tripersonal God.