For me a Christian is a Trinitarian. Do you believe in the Trinity?
If you mean the Trinity as described in the Athanasian Creed, I must confess that I do not understand the doctrine.
That said, I believe in the Father, the Son, and the Holy Spirit, the three being one God.
That's a nice definition but unfortunately it leaves out many of the "Christian Fathers" who are non-trinitarians. Like Hippolytus and Justin Martyr. Other Christian Fathers do not fit the narrow (non-Biblical) definition you have proposed.
From wiki
That the doctrine relies almost entirely on non-Biblical terminology. Some notable examples include: Trinity, Three-in-one, God the Son, God the Holy Ghost, Person in relation to anyone other than Jesus Christ being the image of God's person (hypostasis).
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Restoring_the_Ancient_Church/chap03.html
also Athenagoras, Clement of Alexandria, and Irenaeus
The Subordination of the Son and Spirit Within "orthodox" circles of the pre-Nicene Church, even where terms like "second God" and "angel" were rejected, it was always made clear that the Son and Holy Spirit are subjected to the Father, who is "greater than" them. The various forms of this doctrine are known as "subordinationism," and Bettenson admits that "'subordinationism' . . . was pre-Nicene orthodoxy."153 After all, Jesus said that "My Father is greater than I" (John 14:28), and He asserted that the He does not know the hour of His Second Coming--only the Father knows. (Matthew 24:36) Paul wrote that the Father is "the God and Father of our Lord Jesus Christ" (Romans 15:6, NEB), and revealed that after the resurrection Jesus will "be subject unto him [the Father] that put all things under him, that God may be all in all." (1 Corinthians 15:24-28)
In the post-Apostolic era, Hippolytus wrote that the Father is "the Lord and God and Ruler of all, and even of Christ Himself . . . ."154 And Irenaeus insisted that the Father surpasses the Son in knowledge:
For if any one should inquire the reason why the Father, who has fellowship with the Son in all things, has been declared by the Lord alone to know the hour and the day [of judgment], he will find at present no more suitable, or becoming, or safe reason than this (since, indeed, the Lord is the only true Master), that we may learn through Him that the Father is above all things. For "the Father," says He, "is greater than I."155
Clement of Alexandria taught that while the Father cannot be known, the Son is the object of knowledge:
God, then, being not a subject for demonstration, cannot be the object of science. But the Son is wisdom, and knowledge, and truth, and all else that has affinity thereto. He is also susceptible of demonstration and of description.156
The Fathers maintained a form of "monotheism," however, by asserting the absolute monarchy of the Father as the "only true God." For instance, Irenaeus states:
This, therefore, having been clearly demonstrated here (and it shall yet be so still more clearly), that neither the prophets, nor the Apostles, nor the Lord Christ in His own person, did acknowledge any other Lord or God, but the God and Lord supreme: the prophets and the Apostles confessing the Father and the Son; but naming no other as God, and confessing no other as Lord: and the Lord Himself handing down to His disciples, that He, the Father, is the only God and Lord, who alone is God and ruler of all;--it is incumbent on us to follow, if we are their disciples indeed, their testimonies to this effect.157
Because of the monarchy and harmony within the Godhead, in a sense the diversity of power, rank, and glory was not thought to particularly matter in practice. As Origen put it:
Moreover, nothing in the Trinity can be called greater or less, since the fountain of divinity alone contains all things by His word and reason, and by the Spirit of His mouth sanctifies all things which are worthy of sanctification . . . .158
Likewise, Athenagoras spoke of the "diversity in rank"159 within the Godhead, but qualified this by saying, "The son is in the father and the father is in the son by a powerful unity of spirit . . . ."160