Rene Descartes
René Descartes was a French philosopher, mathematician, and scientist. Dubbed the father of modern western philosophy, much of subsequent Western philosophy is a response to his writings, which are studied closely to this day. He is famous for having made an important connection between geometry and algebra, which allowed for solving geometrical problems by way of algebraic equations. He is also known for his philosophical statement 'Cogito, ergo sum' ('I think, therefore I am').
Books
This list of books are ONLY the books that have been ranked on the lists that are aggregated on this site. This is not a comprehensive list of all books by this author.

1. Meditations on First Philosophy
"Meditations on First Philosophy" is a philosophical treatise that introduces the concept of radical doubt as a foundational element of knowledge. The book is known for the famous philosophical statement, "I think, therefore I am," which the author uses to establish the existence of the self as a necessary truth. The author also presents arguments for the existence of a benevolent God and the immortality of the soul, while examining the differences between the mind and the body, the nature of reality, and the limits of human understanding.
The 582nd Greatest Book of All Time 
2. Discourse on Method
The book is a philosophical and autobiographical treatise that introduces a new form of scientific and philosophical method, which emphasizes on doubt and systematic questioning as the primary means to achieve knowledge. The author argues that by doubting everything, one can then rebuild knowledge, piece by piece, on a more solid foundation. This method is applied to a wide range of topics, including God's existence, the nature of the human mind and body, and the acquisition of knowledge.
The 1249th Greatest Book of All Time 
3. La Géométrie
"La Géométrie" introduces a revolutionary approach to mathematics by merging algebra and geometry into a single discipline. The work outlines the method of using equations to describe geometric shapes and using algebraic formulas to solve geometric problems, thereby laying the groundwork for what is now known as analytic geometry. This treatise fundamentally changed the course of mathematics by providing a systematic framework that allowed for the graphical representation of algebraic equations, and vice versa, thus enabling the precise analysis of geometric spaces using algebra.
The 8726th Greatest Book of All Time