Many point to the earliest Christian writers (aka “Church Fathers”) and decisions by ecumenical councils like Nicea in 325AD., Chalcedon in 451AD as “proof” that Jesus was God.
The truth is that the Bible defines the one God of Israel as Yahweh (in the OT), aka the Father (in the NT). Both Yahweh and Father obviously denote a single Self, individual, in this case a non-human Divine Person.
That’s why the earliest Christian writers and councils consistently speak of the Father as the God, even the one Being (Ousia), without qualification. This was the standard operating procedure up to the so-called Athanasian Creed (6th – 10th century AD).
For example, writing early in the 2nd c. AD., Polycarp calls the Father: “O Lord God Almighty, the Father of your beloved and blessed Son Jesus” (Martyrdom 14).
Justin Martyr says He is “the most true God, the Father and Creator of all….men and gods” (1st Ap. 6, 8, 12, 22, 61).
Irenaeus says that “this Being alone is [the] only God and Lord, who alone is God and ruler of all…one and the same Creator, [the] Lord God of Abraham, and God of Isaac, and God of Jacob and Israel, who art the Father of our Lord Jesus Christ” (Ag. Her. 1.9.2; 2.1; 3.6.4; 3.9.1; 5.18.2; 10.1).
Ignatius “concerning the Father of the universe” says He is “the person of God [who says], I am God, the first [of beings], and I am also the last, and besides Me there is no God, Isaiah 44:6” (To Tarsians 3).
Tertullian, early in the 3rd c. A.D., says that “since He is God, it must necessarily be a unique mark of this quality, that it be confined to One….By possessing these He is God alone, and by His sole possession of them He is One” (Ag. Herm. 4).
And Origen says “The God and Father, who holds the universe together, is superior to every being that exists….the Son, being less than the Father [and] second to the Father; the Holy Spirit is still less….So that in this way the power of the Father is greater than that of the Son and of the Holy Spirit” (On First Principles 1.3).