What is Christus Victor? According to several internet sites (for example, here and here), C.S. Lewis' book The Lion, the Witch, and the Wardrobe expresses a particular understanding of the Atonement, known as Christus Victor.

What are the key points of the Christus Victor understanding of the atonement, and what distinguishes it from other perspectives?
There are several ideas about the atonement that can come under the heading of Christus Victor. Ultimately, the term could apply to any account of the atonement that accords with:


  The work of Christ is first and foremost a victory over the powers which hold mankind in bondage: sin, death and the devil. 1


One of the reasons why it is a bit hard to pin down is that it is basically a narrative viewpoint  - it's a way of telling the story of the atonement, in order to bring people to Christ, and it doesn't necessarily propose a coherent, propositional account of the "mechanics" of atonement. It therefore contrasts, both in style and content, with the satisfaction viewpoints: these not only paint a different picture of the atonement, but they're also more driven by the attempt to give an account that is both rationally justifiable and theologically defensible.

Under the general Christus Victor theme, the Aslan story follows the Ransom Theory of the atonement. This can be traced to the early Fathers, including Origen and Augustine in particular. There is some historical doubt about whether the ransom theory came first, and alternative Christus Victor explanations accreted around it in response to its flaws, or whether ransom theory is one particular systematization of an earlier, more nebulous collection of Christus Victor ideas. In any case, the theory proceeds something like this:


Due to sin, human beings were in bondage to Satan.
Jesus offered himself as a substitute. Since Jesus would be a better prize, Satan accepted; we then become free of his domination. Jesus is the ransom paid to Satan.
But Jesus could not be held by Satan - he escapes death and is resurrected to eternal life.


In Narnia, we see step 1 by the Witch's statement,


  "You know that every traitor belongs to me as my lawful prey, and that for every treachery I have a right to a  kill." 2


and step 3, as told by Aslan, is


  "Though the Witch knew the Deep Magic, there is a magic deeper still which she did not know. [...] when a willing victim who had committed no treachery was killed in a traitor's stead, the Table would crack and death itself would start working backwards." 2


There are some points to criticize about ransom theory in particular (without necessarily invalidating the Christus Victor view in general).


It puts some sort of legitimacy on Satan's claim to us: God appears to be required to pay the ransom. Anselm objected to this.
God wins through trickery, like offering fairy gold that disappears in the morning. This is also hard to square with the legitimacy point: if Satan isn't going to be truly paid, then why bother with the charade of paying the ransom?
Augustine used the metaphor: "The cross of the Lord was the Devil's mousetrap; the bait by which he was caught was the Lord's death" 3, which to some sounds rather impious.
The resurrection is no longer an essential part of the atonement, but more like an added bonus. We are freed as soon as Christ is accepted as a substitute, so he doesn't need to come back to life in order to complete the atonement.


The standard contrasting view is the satisfaction doctrine. Here, the debt is due not to Satan, but to God himself, and it is God's justice (demanding a penalty for sin) that must be met. Christ is the perfect sacrifice, substituted for us, and so justice can be satisfied. This theory has its drawbacks, too. It can make God look tyrannical and bloodthirsty, and there's no obvious link to the life and teaching of Christ - it's all about his death and resurrection. A Christus Victor account places the gospel as part of the victory, according with the central idea of Christ's defeat of sin.

1. Gustaf Aulen, Christus Victor, 1931 (trans. by A. G. Hebert from the Swedish Den kristna försoningstanken, 1930).
2. C. S. Lewis, The Lion, the Witch and the Wardrobe, 1950.
3. Muscipula diaboli, crux domini; esca qui caperetur, mors domini. - Augustine, Sermon 263, beginning On the fortieth day, the ascension of the Lord.