René Descartes: Cogito ergo sum

René Descartes (Latinized form Renatus Cartesius - March 31, 1596 La Haye en Touraine – February 11, 1650 Stockholm) was a French philosopher and mathematician, who has been called the founder of modern philosophy.

He was a rationalist who sought to systematically doubt everything. His aim was to find a sure foundation for certain knowledge. Descartes founded 17th-century continental rationalism, which was later represented by Baruch Spinoza and Gottfried Leibniz.

Descartes' most famous thought is Cogito ergo sum ("I think, therefore I am").