T.H. White's collected fiction on the legend of King Arthur is called The Once and Future King, but it is best known for the first part, The Sword in the Stone, which was made into an acclaimed animated film by Disney in 1963.
This part of the story concerns the young Arthur, called Wart, and his growth from a simple boy to the true king of England. Wart is good-hearted by nature and is not attuned to evil in the world; Merlyn the wizard takes him as an apprentice and teaches him lessons about life and reality.
The most obvious change in Wart's character is in his destiny to pull the sword from the stone and become king. At first, he sees the sword and kingship as a desirable fantasy, a romantic act of heroism that will win him friendship and love. By the end of the book, when he has learned about life, war, and responsibility from Merlyn, Wart still removes the sword, but does so reluctantly; he recognizes the burden of leadership, something he could not fathom earlier. Although he remains a good person, his idealism and naivety are tainted by Merlyn's lessons, which have shown him that people are not always kind, and violence to protect the innocent is sometimes the only moral option.