Did Christians Formulate a Doctrine of the Trinity Before the Council of Nicaea?

A Declaration of Faith, by Gregory Thaumaturgus

There is one God, the Father of the living Word, who is His subsistent Wisdom and Power and Eternal Image:¹⁹ perfect Begetter of the perfect Begotten, Father of the only-begotten Son. There is one Lord, Only of the Only,²⁰ God of God, Image and Likeness of Deity, Efficient Word,²¹ Wisdom comprehensive²² of the constitution of all things, and Power formative²³ of the whole creation, true Son of true Father, Invisible of Invisible, and Incorruptible of Incorruptible, and Immortal of Immortal and Eternal of Eternal.²⁴ And there is One Holy Spirit, having His subsistence²⁵ from God, and being made manifest²⁶ by the Son, to wit to men:²⁷ Image²⁸ of the Son, Perfect Image of the Perfect;²⁹ Life, the Cause of the living; Holy Fount; Sanctity, the Supplier, or Leader,³⁰ of Sanctification; in whom is manifested God the Father, who is above all and in all, and God the Son, who is through all. There is a perfect Trinity, in glory and eternity and sovereignty, neither divided nor estranged.³¹ Wherefore there is nothing either created or in servitude³² in the Trinity;³³ nor anything superinduced,³⁴ as if at some former period it was non-existent, and at some later period it was introduced. And thus neither was the Son ever wanting to the Father, nor the Spirit to the Son;³⁵ but without variation and without change, the same Trinity abideth ever.³⁶

The Nicene Creed

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,
was incarnate from the Holy Spirit and 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 and the Son,
who with the Father and the Son is worshipped and glorified,
who 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.