It seems the earliest teachings on the subject all agree there are "three" when speaking of God. Monarchianism, which has a modern rendition in oneness Pentecostalism (God manifests in three modes of Father, Son, and Spirt), a pre-Nicean trinity, and the view of Arius (there was a time the Son was not,) but his teachings were destroyed. It appears Athanasius, the theologian of the Nicean trinity, applied Platonic philosophy to explain how the Father, Son, and Spirit are in reality.