Dawkins, in GD, writes: "Any God capable of designing anything would have to be complex enough to demand the same kind of explanation in his own right. God presents an infinite regress from which he cannot help us to escape."
Anything that explains something must itself be explained. If God created the universe, then who or what made God? And then, ad infinitum, who or what made that which made God? And so on.
The McGrath's in DD, respond that "the 'holy grail' of the natural sciences is the quest for a 'grand unifed theory' - the 'theory of everything'." (DD, 27) Such a theory is important because can explain everything, without itself requiring an explanation.
So: "If Dawkins's brash and sinmplistic arguments carried weight, this great scientific quest could be dismissed with a seemingly profound yet in fact trivial question: What explains the explainer?" (DD, 27)
Perhaps there is no such theory. But, there are scientists looking to discover it. It is understood, if it exists, to be "the termination of an explanatory process." It is a quest for an irredicuble explanation, and it lies at the heart of the scientific quest. McGrath writes: "There is no logical inconsistency involved, no conceptual flaw, no self-contradiction involved."
Thus, analogously, there is no contradiction invovled in viewing God as the ultimate explanation of the universe.
Further, and saying more here than the McGrath's do, the question "But what caused God?" is a nonsense question if God is understood to be an eternal being, or a being that did not come to be. Whatever begins to exist has a cause. But if something did not begin to exist, then the question as to its "cause" seems misguided. (See William Lane Craig's writings on the Kalam Cosmological Argument for the Existence of God.)