Justin Martyr believed that the Old Testament figure of Yahweh was the Son:
"Apology" Chapter 63:
"No one knoweth the Father, but the Son; nor the Son but the Father, and those to whom the Son will reveal Him."(7) The Jews, accordingly, being throughout of opinion that it was the Father of the universe who spake to Moses, though He who spake to him was indeed the Son of God, who is called both Angel and Apostle, are justly charged, both by the Spirit of prophecy and by Christ Himself, with knowing neither the Father nor the Son. For they who affirm that the Son is the Father, are proved neither to have become acquainted with the Father, nor to know that the Father of the universe has a Son; who also, being the first-begotten Word of God, is even God. And of old He appeared in the shape of fire and in the likeness of an angel to Moses and to the other prophets; but now in the times of your reign,(8) having, as we before said, become Man by a virgin, according to the counsel of the Father, for the salvation of those who believe on Him, He endured both to be set at nought and to suffer, that by dying and rising again He might conquer death. And that which was said out of the bush to Moses, "I am that I am, the God of Abraham, and the God of Isaac, and the God of Jacob, and the God of your fathers,"(9) this signified that they, even though dead, are let in existence, and are men belonging to Christ Himself.
That Christ was the first born of God, as the Word. And this word "Logos" means rationality or reasoning principle, and thus he equates reasonable men as godly men of faith and unreasonable ones as wicked...
But lest some should, without reason, and for the perversion of what we teach, maintain that we say that Christ was born one hundred and fifty years ago under Cyrenius, and subsequently, in the time of Pontius Pilate, taught what we say He taught; and should cry out against us as though all men who were born before Him were irresponsible—let us anticipate and solve the difficulty. We have been taught that Christ is the first-born of God, and we have declared above that He is the Word of whom every race of men were partakers; and those who lived reasonably(5) are Christians, even though they have been thought atheists; as, among the Greeks, Socrates and Heraclitus, and men like them; and among the barbarians, Abraham, and Ananias, and Azarias, and Misael, and Elias, and many others whose actions and names we now decline to recount, because we know it would be tedious. So that even they who lived before Christ, and lived without reason, were wicked and hostile to Christ, and slew those who lived reasonably. But who, through the power of the Word, according to the will of God the Father and Lord of all, He was born of a virgin as a man, and was named Jesus, and was crucified, and died, and rose again, and ascended into heaven, an intelligent man will be able to comprehend from what has been already so largely said.
Christ is the Word and First-begotten
that we claim to be acknowledged, not because we say the same things as these writers said, but because we say true things: and (secondly) that Jesus Christ is the only proper Son who has been begotten by God, being His Word and first-begotten, and power; and, becoming man according to His will, He taught us these things for the conversion and restoration of the human race:
The whole work is here.