The philosopher known for the phrase "I think, therefore I am" (Cogito, ergo sum) is René Descartes. A 17th-century French philosopher and mathematician, Descartes is often referred to as the father of modern philosophy. His famous statement encapsulates his approach to philosophy, asserting that the very act of doubt or thinking implies the existence of the self as a thinking being. Descartes sought to establish a foundation for scientific knowledge by emphasizing reason and skepticism. His work laid the groundwork for various fields, including mathematics and psychology, and continues to influence philosophical thought today.