Descartes: Diagram showing the ventricles of the brain (E) and pineal gland (H). A & B are fibers ending in walls of ventricles. Illustration from 1664. Rene Descartes, French mathematician and philosopher (31st March 1596 - 11 February 1650). Descartes created co-ordinate geometry, a bridge between algebra and geometry, now known as Cartesian geometry. He is considered a founding father of modern philosophy, famous for his statement "Cogito ergo sum" - "I think, therefore I am" (from his 'Discourses on the Method' 1637).