In this post, some quotes from Irenaeus, late 2nd c. bishop famous for his long treatise against the various gnostics.
I have not modified the translations, other than adding bold type. Some of the clarifying insertions [in brackets] are by the translators, others by me.
Wherefore I do also call upon thee, LORD God of Abraham, and God of Isaac, and God of Jacob and Israel, who art the Father of our Lord Jesus Christ, the God who, though the abundance of Thy mercy, hast had a favour towards us, that we should know Thee, who hast made heaven and earth, who rulest over all, who art the only and the true God, above whom there is none other God; grant, by our Lord Jesus Christ, the governing power of the Holy Spirit; give to every reader of this book to know Thee, that Thou art God alone, to be strengthened in Thee, and to avoid every heretical, and godless, and impious doctrine. Against Heresies III.6.4, p. 419.
…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 Son; but naming no other as God [than the Father], and confessing no other as Lord [than the Son]: and the Lord Himself [i.e. Jesus] 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. …[Jesus] did not declare to them another God, besides Him who made the promise to Abraham… There is therefore one and the same God, the Father of our Lord, who also promised, through the prophets, that He would send His forerunner [i.e. John the Baptist]; and His salvation – that is, His Word – He caused to be made visible to all flesh, [the Word] Himself being made incarnate… Against Heresies III.9.1, p. 422.
Next, an interesting deception argument, directed particularly against the gnostic Marcion, who taught that the god of the Old Testament was an evil and inferior deity to the one true God taught by Jesus.
Now to whom is it not clear, that if the Lord [Jesus] had known many fathers and gods, He would not have taught His disciples to know [only] one God, and to call Him alone Father? But He did the rather distinguish those who by word merely (verbo tenus) are termed gods, from Him who is truly God, that they should not err as to His doctrine, nor understand one [in mistake] for another. And if He did indeed teach us to call one Being Father and God, while he does from time to time Himself confess other fathers and gods in the same sense, then He will appear to enjoin a different course upon His disciples from what He follows Himself. Such conduct, however, does not bespeak the good teacher, but a misleading and invidious one. The apostles too, according to these men’s showing, are proved to be transgressors of the commandment, since they confess the Creator as God, and Lord, and Father, as I have shown – if He is not alone God and Father. Jesus, therefore, will be to them the author and teacher of such transgression, inasmuch as He commanded that one Being should be called Father, thus imposing upon them the necessity of confessing the Creator as their Father, as has been pointed out. Against Heresies IV.1.2, p. 463.
Later in the book:
Both the Lord [Jesus], then, and the apostles announce as the one only God the Father, Him who gave the law, who sent the prophets, who made all things; and therefore does He say [in the parable in Matthew 22], “He sent his armies,” because every man, inasmuch as he is a man, is His workmanship, although he may be ignorant of his God. For He gives existence to all; He, “who maketh His sun to rise upon the evil and the good, and sendeth rain upon the just and unjust.” [Luke 15:11] Against Heresies IV.36.6, p. 517.
In the one God here one and the same as Father (unitarian)?
Or is the one God here a tripersonal deity consisting of or somehow containing three equally divine persons? (trinitarian)
You be the judge.