Tertullian (240 AD) was a Trinitarian

The first man often credited with using the word "Trinity" was a Trinitarian not an Arian as some allege (Theophilus of Antioch (168-181/188 A.D.) was actually the first person to use the word 'Trinity' Theophilus to Autolycus book 2 ch.15 p.101). This can be proven easily when we study his writings. He believed Christ in His preexistence and deity was the personal eternal Word "with" God (rather than eternal Son). Tertullian was born in 160 AD and died in 220 AD, long before Nicaea (325 AD). He even wrote that Christ was "man and God".

Here are the quotes for your convenience:

“We believe that there is one only God, but under the following dispensation, or oi0konomi/a, as it is called, that this one only God has also a Son, His Word, who proceeded from Himself, by whom all things were made, and without whom nothing was made. Him we believe to have been sent by the Father into the Virgin, and to have been born of her-being both Man and God, the Son of Man and the Son of God, and to have been called by the name of Jesus Christ... " (Against Praxeas, Chapter 2)

“...is still guarded, which distributes the Unity into a Trinity, placing in their order the three Persons – the Father, the Son, and the Holy Ghost: three, however, not in condition, but in degree; not in substance, but in form; not in power, but in aspect; yet of one substance, and of one condition, and of one power, inasmuch as He is one God, from whom these degrees and forms and aspects are reckoned, under the name of the Father, and of the Son, and of the Holy Ghost. How they are susceptible of number without division, will be shown as our treatise proceeds.” (Against Praxeas, Chapter 2)

"The origins of both his substances display him as man and as God: from the one, born, and from the other, not born" (The Flesh of Christ, 5:6-7).

Against Praxeas, Chapter 5:
“Thus, in a certain sense, the word is a second person within you, through which in thinking you utter speech, and through which also, (by reciprocity of process,) in uttering speech you generate thought. The word is itself a different thing from yourself.” [Continued:] “I may therefore without rashness first lay this down (as a fixed principle) that even then before the creation of the universe God was not alone, since He had within Himself both Reason, and, inherent in Reason, His Word, which He made second to Himself by agitating it within Himself.”
“There are some who allege that even Genesis opens thus in Hebrew: In the beginning God made for Himself a Son. As there is no ground for this, I am led to other arguments derived from God's own dispensation, in which He existed before the creation of the world, up to the generation of the Son. For before all things God was alone— being in Himself and for Himself universe, and space, and all things. Moreover, He was alone, because there was nothing external to Him but Himself. Yet even not then was He alone; for He had with Him that which He possessed in Himself, that is to say, His own Reason. For God is rational, and Reason was first in Him; and so all things were from Himself. This Reason is His own Thought (or Consciousness) which the Greeks call λόγος, by which term we also designate Word or Discourse and therefore it is now usual with our people, owing to the mere simple interpretation of the term, to say that the Word was in the beginning with God”

RAPID FIRE VERSES: The Eternal Son:

http://www.youtube.com/watch?v=Q8aYaX...