According to the following source re the Gnostic Valentinus:
“In the fourth century, Marcellus of Ancyra declared that the idea of the Godhead existing as three hypostases (hidden spiritual realities) came from Plato through the teachings of Valentinus,[10] who is quoted as teaching that God is three hypostases and three prosopa (persons) called the Father, the Son, and the Holy Spirit:”
" “Now with the heresy of the Ariomaniacs, which has corrupted the Church of God… These then teach three hypostases, just as Valentinus the heresiarch first invented in the book entitled by him ‘On the Three Natures’. For he was the first to invent three hypostases and three persons of the Father, Son and Holy Spirit, and he is discovered to have filched this from Hermes and Plato.[11]” "
“Since Valentinus had used the term hypostases, his name came up in the Arian disputes in the fourth century. Marcellus of Ancyra was a staunch opponent of Arianism, but also denounced the belief in God existing in three hypostases as heretical, and was later condemned for his teachings. Marcellus attacked his opponents (On the Holy Church, 9) by linking them to Valentinus:”
" “Valentinus, the leader of a sect, was the first to devise the notion of three subsistent entities (hypostases), in a work that he entitled On the Three Natures. For, he devised the notion of three subsistent entities and three persons — father, son, and holy spirit.[12]” "
“It should be noted that the Nag Hammadi library Sethian text Trimorphic Protennoia identifies Gnosticism as professing Father, Son, and feminine wisdom Sophia or as Professor John D. Turner denotes, God the father, Sophia the mother, and Logos the son.”
en.wikipedia.org/wiki/Valentinus_(Gnostic