Rene Descartes

René Descartes was a seventeenth-century French philosopher and mathematician, often called the father of modern philosophy.

His statement Cogito, ergo sum—I think, therefore I am—established the thinking self as the foundation of knowledge.

Descartes developed the coordinate system that bears his name, linking algebra to geometry.

Cartesian refers to his methods and ideas: Cartesian doubt, Cartesian coordinates.