So, again, I ask, to whom was the ransom paid if it is a literal ransom? As St. Gregory says, the one who held us in bondage is the evil one, so did he receive the ransom?
The problem with viewing terms like "ransom" and "atonement" too literally is that doing so imprisons God. Basically, it means God cannot forgive sin unless an atonement is made or a ransom paid.
At least in the usual Catholic understanding, God can do what he wants. He could have remitted all sin freely, but he chose Christ's sacrificial atonement as the way to accomplish it. Anselm thought it was necessary to fulfill the demands of true divine justice, but Abelard and Aquinas and most other Catholic theologians denied it was absolutely necessary.
As for the ransom theory, I thought the Catholic Encyclopedia article had an excellent discussion of it:
The restoration of fallen man was the work of the Incarnate Word. "God was in Christ reconciling the world to himself" (2 Corinthians 5:19). But the peace of that reconciliation was accomplished by the death of the Divine Redeemer, "making peace through the blood of His cross" (Colossians 1:20). This redemption by death is another mystery, and some of the Fathers in the first ages are led to speculate on its meaning, and to construct a theory in explanation. Here the words and figures used in Holy Scripture help to guide the current of theological thought. Sin is represented as a state of bondage or servitude, and fallen man is delivered by being redeemed, or bought with a price. "For you are bought with a great price" (1 Corinthians 6:20). "Thou art worthy, O Lord, to take the book, and to open the seals thereof; because thou wast slain, and hast redeemed to God, in thy blood" (Revelation 5:9). Looked at in this light, the Atonement appears as the deliverance from captivity by the payment of a ransom. This view is already developed in the second century. "The mighty Word and true Man reasonably redeeming us by His blood, gave Himself a ransom for those who had been brought into bondage. And since the Apostasy unjustly ruled over us, and, whereas we belonged by nature to God Almighty, alienated us against nature and made us his own disciples, the Word of God, being mighty in all things, and failing not in His justice, dealt justly even with the Apostasy itself, buying back from it the things which were His own" (Irenaeus Aversus Haereses V, i). And St. Augustine says in well-known words: "Men were held captive under the devil and served the demons, but they were redeemed from captivity. For they could sell themselves. The Redeemer came, and gave the price; He poured forth his blood and bought the whole world. Do you ask what He bought? See what He gave, and find what He bought. The blood of Christ is the price. How much is it worth? What but the whole world? What but all nations?" (Enarratio in Psalm xcv, n. 5).
It cannot be questioned that this theory also contains a true principle. For it is founded on the express words of Scripture, and is supported by many of the greatest of the early Fathers and later theologians. But unfortunately, at first, and for a long period of theological history,
this truth was somewhat obscured by a strange confusion, which would seem to have arisen from the natural tendency to take a figure too literally, and to apply it in details which were not contemplated by those who first made use of it. It must not be forgotten that the account of our deliverance from sin is set forth in figures. Conquest, captivity, and ransom are familiar facts of human history. Man, having yielded to the temptations of Satan, was like to one overcome in battle. Sin, again, is fitly likened to a state of slavery. And when man was set free by the shedding of Christ's precious Blood, this deliverance would naturally recall (even if it had not been so described in Scripture) the redemption of a captive by the payment of a ransom.
But however useful and illuminating in their proper place, figures of this kind are perilous in the hands of those who press them too far, and forget that they are figures. This is what happened here. When a captive is ransomed the price is naturally paid to the conqueror by whom he is held in bondage.
Hence, if this figure were taken and interpreted literally in all its details, it would seem that the price of man's ransom must be paid to Satan. The notion is certainly startling, if not revolting. Even if brave reasons pointed in this direction, we might well shrink from drawing the concluslon. And this is in fact so far from being the case that it seems hard to find any rational explanation of such a payment, or any right on which it could be founded. Yet, strange to say, the bold flight of theological speculation was not checked by these misgivings. In the above-cited passage of St. Irenaeus, we read that the Word of God "dealt justly even with the Apostasy itself [i.e. Satan], buying back from it the things which were His own." This curious notion, apparently first mooted by St. Irenaeus, was taken up by Origen in the next century, and for about a thousand years it played a conspicuous part in the history of theology. In the hands of some of the later Fathers and medieval writers, it takes various forms, and some of its more repulsive features are softened or modified. But the strange notion of some right, or claim, on the part of Satan is still present. A protest was raised by St. Gregory of Nazianzus in the fourth century, as might be expected from that most accurate of the patristic theologians. But it was not till St. Anselm and Abelard had met it with unanswerable arguments that its power was finally broken.