No one has ever seen God; the only God, who is at the Father's side, he has made him known. (John 1:18, ESV)In this verse, the one "who is at the Father's side" is referred to as "the only God." Two persons in this passage are referred to as God.
Even though men like Moses saw glimpses of God in the Old Testament, nobody has seen the full revelation of God, until now. When God became flesh, the ultimate revelation of God for us humans, He came as the person of Jesus. The ultimate revelation of God from before time, is known to us as Jesus.