Especially in light of the misnamed “Athanasian Creed” and its consistent usage by semi-modalists to sum up their belief, it would perhaps not be difficult to suppose that Athanasius believed that version of pseudo-trinitarianism that passes for the doctrine of the Trinity since the time of Augustine: the variant of modalism I have taken to calling semi-modalism.
But actually, Athanasius very explicitly supported the biblical doctrine that the one God is the Father of the Lord Jesus Christ. This should not surprise us at all when we consider that Athanasius not only helped frame, but also spent his life defending the Nicene Creed, which very explicitly defines that the identity of the one God is the person of the Father.
In truth if there is really a creed that deserves the label “Athanasian”, it is the Nicene Creed, given all that Athanasius sacrificed to defend and champion it. But here are several quotes from various writing of Athanasius in which his belief in this point of doctrine can also be seen. Let’s examine some highlights from among them:
“He it is who through His Word made all things small and great, and we may not divide the creation, and says this is the Father’s, and this the Son’s, but they are of one God, who uses His proper Word as a Hand, and in Him does all things. This God Himself shews us, when He says, ‘All these things hath My Hand made;’ while Paul taught us as he had learned, that ‘There is one God, from whom all things; and one Lord Jesus Christ, through whom all things.” (Defense of the Nicene Definition, Chapter III.)
Here we see Athanasius argue that all creation cannot be divided up into what was created by God versus what what created by His Son, but that rather we must understand that all creation is the work of the one God- the Father- through His one Son, His Word. Notice that he explicitly speaks of the Word here as the Word of the one God, clearly equating the one God and the Father, using the names “one God” and “Father” as synonymous.
”But if this is not to be seen, but while the creatures are many, the Word is one, any one will collect from this, that the Son differs from all, and is not on a level with the creatures, but proper to the Father. Hence there are not many Words, but one only Word of the one Father, and one Image of the one God.” (Against the Arians, Discourse II.)
Here again we see a direct equation made between the “one Father” and the “one God”. The following quotes are also clear on this:
“For there is One God, and not many, and One is His Word, and not many; for the Word is God, and He alone has the Form of the Father.” (Against the Arians, Discourse III.)
“For the Word, being Son of the One God, is referred to Him of whom also He is; so that Father and Son are two, yet the Monad of the Godhead is indivisible and inseparable. And thus too we preserve One Beginning of Godhead and not two Beginnings, whence there is strictly a Monarchy” (Against the Arians, Discourse IV.)
“For the one God makes and creates; but Him He begets from Himself, Word or Wisdom.” (Against the Arians, Discourse IV.)
“The Triad, then, although the Word took a body from Mary, is a Triad, being inaccessible to addition or diminution; but it is always perfect, and in the Triad one Godhead is recognised, and so in the Church one God is preached, the Father of the Word.” (To Epictetus)
If you would like to see more of these quotes from not only Athanasius himself, but many other church fathers, please see my extensive collection of them available for viewing here: https://nicenefaith.wordpress.com/2017/03/08/i-believe-in-one-god-the-father-almighty/