While we encounter it also in the Old Testament as in let us make man in our own image, the Holy Trinity was fully revealed to the Apostles by Christ as seen in “Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit.”
I think it’s safe to summarize the history afterward as the Church rejecting what it is not as the need arose with the teachers of heresies.
Thanks for the answer though I'm a little surprised by it. :-)
Are you suggesting that the doctrine of the trinity as traditional Christianity understands it today is fully established and explained in scripture? That the Catholic church played no part in it's explanation, formulation or clarification?