The historical figure known for saying, "I think, therefore I am," is René Descartes, a French philosopher, mathematician, and scientist. This statement, "Cogito, ergo sum" in Latin, is a foundational element of Western philosophy, emphasizing doubt and the act of thinking as proof of existence. Descartes used this phrase to argue that the very act of thinking is evidence of one's own existence, thus establishing a basis for knowledge beyond the external world. His work, particularly in the realms of metaphysics and epistemology, laid the groundwork for modern philosophy and has influenced countless thinkers and disciplines, including science and mathematics.