Rene Descartes was a philosopher, mathematician, physicist and all-round genius who lived in the seventeenth century. He is often described as the father of modern philosophy. He was the first Western philosopher in a long time to try to work it all out himself, rather than relying on the authority of the great ancient philosophers like Plato and Aristotle, or on divine revelation. His Meditations on First Philosophy was one of the most important books in the history of philosophy, and is still widely read. You should check it out.