Alberto Knox is a major character in Sophie's World who acts as Sophie Amundsen's philosophy teacher throughout the book.

Initially, Alberto begins by sending letters to Sophie, summarizing the ancient and classical philosophers. However, eventually they meet in person. Alberto cares about Sophie and acts as a sort of father figure for her, and he guides her through the lessons. He is always able to answer Sophie's questions, and he wisely listens to Sophie during her lectures. Alberto displays humility, and he always learns to adapt and accept facts as events emerge. As a philosopher, he employs logic and reason to think things through and he shows great wisdom and often knows everything going on. Alberto is able to surmise that he and Sophie were a part of Albert Knag's novel, and he assumes that they'll be able influence his subconscious. Even after he finds out he is a spirit in reality, he keeps calm and holds on to his beliefs, and he manages to theorize a reason of his and Sophie's existence. By the end of the novel, Sophie becomes his equal in philosophy, thus proving the effectiveness of his teaching.