The Son of God is the Lord Jesus Christ, the first Man that was 100% begotten out of God.
"No one has ascended to heaven but He who came down from heaven, that is, the Son of Man [who is in heaven]."
"When Jesus came into the region of Caesarea Philippi, He asked His disciples, saying,
“Who do men say that I, the Son of Man, am?”
So they said, “Some say John the Baptist, some Elijah, and others Jeremiah or one of the prophets.” He said to them, “But who do you say that I am?” Simon Peter answered and said,
“You are the Christ, the Son of the living God.”"