The Nicene Creed was negotiated by the Councils of Nicea in the Fourth Century, and it is the “epitome” of the doctrine of the Trinity. Before that time, various Christian groups disagreed as to whether the Godhead was one acting as three, or three acting as one. The Council of Nicea settled on the former.
Obviously, not all those who have read the “Nicene Creed” or carry it around with them agree with the fact that God is one Power, 3 distinct personalities: the Father, the Son, and the Holy Spirit, a Triune God.
Believing anything different makes it into a polytheistic religion. And I worship One God: the eternal I AM.