Who is famous for "Cogito ergo sum" (I think therefore I am)?

'Cogito ergo sum' (I think, therefore I am) is the famous philosophical statement by Rene Descartes, found in his work 'Discourse on the Method' (1637). This became the foundation of his philosophy, establishing that the very act of doubting one's existence proves that there must be a doubter (a thinking self) doing the doubting. Euclid was a mathematician, John von Neumann a 20th century mathematician, and Isaac Newton a physicist.