Descartes was a philosopher who lived in the 17th century. He is known for his contributions to the development of modern philosophy, particularly in the areas of epistemology and metaphysics. Descartes is famous for his method of doubt, which he used to establish a foundation of knowledge that could not be doubted. He is also known for his theory of mind-body dualism, which posits that the mind and body are two separate entities that interact with each other. Descartes's philosophy has had a significant impact on the development of Western philosophy, and his ideas continue to be studied and debated by philosophers today.