https://en.wikipedia.org/wiki/Theophilus_of_Antioch
"Trinity
Theophilus's apology is most notable for being the earliest extant Christian work to use the word "Trinity" (Greek: τριάς
trias), although it does not use the common formula of "the Father, the Son, and the Holy Spirit" to describe the Trinity. Rather, Theophilus himself puts it as "God, his Word (Logos) and his Wisdom (Sophia),"
[19] perhaps following the early Christian practice of identifying the Holy Spirit as the Wisdom of God, as he seems to demonstrate in his interpretation of Psalm 33:6,
[20] and which is also expressed in the works his contemporary,
Irenaeus of Lyon, who commenting on that selfsame verse writes,
“By the word of the Lord were the heavens established, and by his spirit all their power." Since then the Word establishes, that is to say, gives body and grants the reality of being, and the Spirit gives order and form to the diversity of the powers; rightly and fittingly is the Word called the Son, and the Spirit the Wisdom of God.
[21]
This practice served as a way to express Christian doctrine in a way that is more relatable to contemporary views
—to ideas found in Greek philosophy or
Hellenistic Judaism in which such concepts as
Nous (Mind),
Logos (Word, Reason) and
Sophia (Wisdom) were common. As the
Patripassionist heresies arose, however, the formula of "Father, Son, Holy Spirit" became more prominently featured, as such beliefs denied the persons of the
Economy (an earlier developed term for the Trinity). As Theophilus does not appear to be introducing the word Trinity in novel fashion, it is probable that the word was in use before this time.
[22] The context for his use of the word
Trinity is commentary on the successive work of the creation weeks (Genesis chapters 1-3), where Theophilus expresses the
Trinity as follows:
In like manner also the three days which were before the luminaries, are types of the Trinity, of God, and His Word, and His wisdom. And the fourth is the type of man, who needs light, that so there may be God, the Word, wisdom, man.
— Theophilus
[23]
The concept of intermediate divine beings was common to Platonism and certain Jewish sects. In
Proverbs 8 Wisdom (as feminine consort) is described as God's Counsellor and Workmistress, who dwelt beside Him before the creation of the world."
So our earliest proponents of Trinity include this Theophilus of Antioch, of which we have only one piece of writing, Tertullian (who later went Montanist on us) and Origen (who contributed the idea that the Son is being eternally generated by the Father). Origen was posthumously excommunicated by the ancient church 2 centuries after he died, I think it was for saying that it might be possible for the devil to repent and be saved.
Athanasius and the Cappadocian Trio of Basil, Gregory of Nazianzus (sp) and Gregory of Nyssa all contributed much to amplifying a doctrine of Trinity -- by then we are in the 4th century -- the big battle of Athanasius against Arius was that the Son was same essence as the Father. There were several "lead changes" in this battle as the arch heretic Arius kept getting an upper hand, I mean the opinion of people including Constantine was going back and forth from supporting Athanasius and Arius.