The council of Nicea (325 A.D.) was not the first Christian creed and was not the first time Christians affirmed the Divinity of Jesus. In fact, Jesus was believed to be God by the earliest Christians as seen in Paul (1 Cor. 8:6 [40-55 A.D.]; Phil. 2:5-11 [40-60 A.D.]; 1 Cor. 1:2; 16:22 [40-60 A.D.]) and taught by Jesus in the Gospels: Mark (Mk. 2:5-11 [55-70 A.D.]), Matthew (Mt. 2:2; 28:9 [60-80 A.D.]), Luke ([60-80 A.D.]), and John (John 5:18; 14:9; cf. John 20:28 [90-100 A.D.]). Also, Hebrews and Revelation.
325 A.D. - Creed #3
The Council of Nicea occurred in 325 A.D. in which the following creed was adopted
We believe in one God, the Father, the Almighty, maker of heaven and earth, of all that is, seen and unseen.
We believe in one Lord, Jesus Christ, the only Son of God, eternally begotten of the Father, God from God, Light from Light, true God from true God, begotten, not made, of one Being with the Father. Through him all things were made. For us and for our salvation he came down from heaven: by the power of the Holy Spirit he became incarnate from the Virgin Mary, and was made man. For our sake he was crucified under Pontius Pilate; he suffered death and was buried. On the third day he rose again in accordance with the Scriptures; he ascended into heaven and is seated at the right hand of the Father. He will come again in glory to judge the living and the dead, and his kingdom will have no end.
We believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father. With the Father and the Son he is worshiped and glorified. He has spoken through the Prophets. We believe in one holy catholic and apostolic Church. We acknowledge one baptism for the forgiveness of sins. We look for the resurrection of the dead, and the life of the world to come. Amen.
The most controversial parts about Jesus are underlined. They include the fact that Jesus is (1) the only or unique Son of God, (2) God from God or God the Son sent by God the Father, (3) begotten, not made The simple fact is that Jesus was not first beleived to be divine at the Council of Nicea. In fact, from the beginnings of the Christian movement, we see that Jesus was already believed to be Divine.
40-55 A.D. - Creed #2
The Council of Nicea was not the first creed. In 55 A.D., Paul records and adapts an early Jewish creed, but Christianizes it, Paul states,
"4 Therefore concerning the eating of things sacrificed to idols, we know that there is no such thing as an idol in the world, and that there is no God but one. 5 For even if there are so-called gods whether in heaven or on earth, as indeed there are many gods and many lords, 6 yet for us there is but one God, the Father, from whom are all things and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him."
Remarkably, Paul takes the Jewish statement of faith called the Shema and applies it to Jesus. The Shema states, ""Hear, O Israel! The LORD is our God, the LORD is one!" Paul says, "yet for us there is but one God...and one Lord, Jesus Christ... (1 Cor. 8:6)."Every Orthodox Jewish person is supposed to recite the Shema daily. This is the theme verse for Judaism which held to monotheism or the idea that there is only one God.
By Paul including Jesus within the Divine Identity of God as expressed in the Shema, he is essentially saying that Jesus is God. In essence, Jesus created all things as Paul states in 1 Corinthians 8:6b, "one Lord, Jesus Christ, by whom are all things, and we exist through Him." Jesus is seen as the Creator just like the council of Nicea says. So, already the notion of Jeus being God and being the Creator are taught by Paul in 55 A.D.
40-60 A.D. - Creed #1
However, 1 Corinthians 8:4-6 is not all that Paul had to say about Jesus. In Philippians 2:6-11 Paul records the following early Christian hymn,
"5 Have this attitude in yourselves which was also in Christ Jesus, 6 who, although  He existed in the form of God,  did not regard equality with God a thing to be grasped, 7 but  emptied Himself,  taking the form of a bond-servant, and  being made in the likeness of men. 8  Being found in appearance as a man,  He humbled Himself by becoming obedient to the point of death, even death on a cross. 9 For this reason also,  God highly exalted Him, and  bestowed on Him the name which is above every name, 10  so that at the name of Jesus EVERY KNEE WILL BOW, of those who are in heaven and on earth and under the earth, 11  and that every tongue will confess that Jesus Christ is Lord, to the glory of God the Father."
This passage is considered to be a hymn that pre-dates Paul. Paul wrote Philippians around 60 A.D., but he records this hymn which has to date earlier that 60 A.D. This passage says Jesus existed in the form of God or that He was God.
When the passage speaks of Jesus being "made" in the likeness of men it is talking not about Jesus coming into existence by creation (which the Council of Nicea rejects), but taking on human flesh. In other words, the hymn is saying that Jesus pre-existed in heaven and he was "made" or "took on" human flesh.