René Descartes was a French philosopher, mathematician, and scientist widely regarded as the "Father of Modern Philosophy." He is one of the most important figures in the history of Western thought, known for his foundational philosophical statement, "I think, therefore I am" (Cogito, ergo sum), and for developing Cartesian dualism. In mathematics, his work established analytic geometry by linking algebra and Euclidean geometry, giving rise to the Cartesian coordinate system. His legacy marks a critical shift toward modern, rationalist inquiry.