List the main characters and make a one sentence description about them.

Here are some of the main characters in "Sophie's World" by Jostein Gaarder, along with one-sentence descriptions:

1. Sophie Amundsen: The young protagonist who receives mysterious philosophical letters and embarks on a journey to explore the history of philosophy.

2. Alberto Knox: Sophie's philosophical mentor who introduces her to the world of philosophy and guides her through its history.

3. Hilde Møller Knag: Hilde is the daughter of Major Albert Knag, and her story parallels Sophie's as she receives a philosophical narrative from her father.

4. Major Albert Knag: Hilde's father and a philosopher who is responsible for creating the philosophical narrative sent to Hilde.

5. Alberto Hilde Knag: An alternate version of Alberto Knox created by Major Knag within his narrative for Hilde.

6. Bishop Berkeley: A historical philosopher whose ideas on idealism and the nature of reality are explored in the book.

7. Aristotle: An ancient Greek philosopher whose works and ideas on ethics, politics, and metaphysics play a significant role in the story.

8. Socrates: A famous philosopher known for his method of questioning and his influence on subsequent philosophical thought.

9. Plato: A student of Socrates and a philosopher who founded the Academy in Athens; known for his philosophy on forms and justice.

10. Jean-Jacques Rousseau: An Enlightenment philosopher whose thoughts on education and society are discussed in the narrative.

11. Baruch Spinoza: A philosopher who examined questions about the existence of God and the nature of reality.

12. Immanuel Kant: A prominent philosopher whose ideas on ethics, metaphysics, and epistemology are central to the book's exploration of modern philosophy. These are some of the key characters in "Sophie's World," and each contributes to the exploration of various philosophical ideas and traditions throughout the novel.