IRENAEUS
He is noted for his role in guiding and expanding Christian communities in what is now the south of France and, more widely, for the development of Christian theology by combating heresy and defining orthodoxy. Originating from Smyrna, now Izmir in Turkey, he had heard the preaching of Polycarp, who in turn was said to have heard John the Evangelist.
Youtube Videos on Irenaeus (6)
Church Father, 
Polycarp, Justin Martyr, Ignatius, 
Polycarp, Justin Martyr or FAQ on Irenaeus (1)
1.What do Christian 'Trinity' scholars say about the Old Testament?
Many theologians, including this analysis of Trinity dogma, note that the Old Testament does not explicitly contain the Trinity, which they believe was only fully revealed later.
The distinguished Trinitarian scholar Bertrand de Margerie in his book The Christian Trinity in History writes:
'Contemporary exegetes [Bible teachers] affirm unanimously that the Old Testament did not bring to the Jewish people a clear and distinct Revelation of the existence of a plurality of persons in God. In this they agree with the clear and frequent affirmation of Fathers such as Irenaeus, Hilary, and Gregory of Nazianzus: that the doctrine of the Trinity is revealed only in the New Testament.'
So any person who lived before Jesus' ministry did not have to believe in the Trinity to be saved because the Trinity is not mentioned in the Old Testament.
