The philosopher known for saying "I think, therefore I am" is René Descartes. This statement, originally phrased in Latin as "Cogito, ergo sum," is a fundamental element of his philosophy and represents a pivotal moment in the history of Western thought. Descartes used this phrase as a foundational element in his work to establish a basis for knowledge and certainty. He sought to doubt everything that could possibly be doubted and concluded that the very act of doubt confirmed his existence as a thinking being. This idea laid the groundwork for modern philosophy and the exploration of consciousness.