René Descartes was a French philosopher, mathematician, and scientist who is often referred to as the "Father of Modern Philosophy." He is best known for his famous statement "Cogito, ergo sum" (I think, therefore I am), which is a fundamental element of his philosophy. Descartes made significant contributions to the fields of mathematics and science, particularly in the development of analytical geometry and the formulation of the laws of refraction. His work had a profound impact on the development of modern philosophy and science.