In Fillory, Aslan is dead. And in fact, he was killed by Martin Chatwin, who started out as a young bright eyed British naif who wanted perfection, badly. So badly that he kept looking but could not find, and turned inward and ravenous upon himself, and ultimately convinced himself that it would be obtainable if he could just deny the old disappointing world with enough might. And so he did, and so he became a monster.
The fascinating thing about Martin is that he’s the logical end of Quentin and all the rest of the snarky kids at Brakebills; he’s evil, but not unrecognizably so. H’s mostly just all this adolescent pain given force. Quentin believes in magic, Janet is bitterly, bitterly disappointed when Ember turns out not to be an omnipotent version of Dumbledore, and it’s the petulant and disappointed rage of these two folks, combined with the almost pitiful optimism of Penny and the insecurity of Josh and the laziness of Eliot (all just other manifestations of this same longing), which brings us to the final tragedies of the story.
— An interesting segment from Matthew Bowman’s article: “The Magicians and the Spiritual Longing of America’s Youth,” Patheos.
As always, spoilers! (And, please forgive some uncited quotes that I was unable to locate in the book at the time of typing of this up).