Which novel features the characters Aslan and Lucy?

The Lion, the Witch and the Wardrobe, published in 1950 - the first of the Narnia books written and the second in the internal chronology, which is why the reading order is permanently argued about. Lewis himself, asked by a boy which was right, said he thought the chronological order was probably better, which the publishers took as settling it and many readers do not.

It began with an image rather than a plan. Lewis said he had carried a picture in his head since he was sixteen of a faun carrying parcels and an umbrella in a snowy wood, and only much later worked out what it belonged to. Evacuee children were staying at his house during the war, which supplied the frame.

Tolkien, his close friend, disliked it. He objected to the mixing of mythologies - fauns, Father Christmas, talking beavers and Norse giants in one wood - as a failure of the internal consistency he cared about above almost everything, and he thought the Christian allegory too obvious. Lewis wrote the whole thing in a few months while Tolkien spent decades on The Lord of the Rings, which tells you something about both of them, and their friendship cooled over it.