The famous philosopher who served as a mentor to Alexander the Great was Aristotle. Aristotle was a renowned Greek philosopher who studied under Plato and later became the tutor of Alexander, who was a student of King Philip II of Macedon. Aristotle imparted knowledge in a variety of subjects such as philosophy, ethics, and sciences, fundamentally shaping Alexander’s worldview. This mentorship played a crucial role in Alexander's development as a leader and military strategist, influencing his later conquests and his appreciation for Greek culture, philosophy, and science throughout his empire.