Arthur Penhaligon is the main character in the fantasy series "The Keys to the Kingdom" by Garth Nix. He is a young boy who unexpectedly becomes the heir to a mysterious and magical realm known as the House. Arthur is characterized by his bravery and determination as he navigates the challenges of this strange world. Throughout the series, Arthur encounters various unique characters and creatures, each representing different aspects of the House. He must solve puzzles and confront powerful foes to reclaim his rightful place and protect both the House and his own world.