Whose quote is I think, therefore I am?

René Descartes wrote je pense, donc je suis in his Discourse on the Method, published in French in 1637. The Latin version, cogito, ergo sum, appeared in his Principles of Philosophy in 1644. Descartes was searching for something he could not doubt, and concluded that the very act of doubting proved he existed as a thinking being. Often called the father of modern philosophy, he was also a brilliant mathematician who created the Cartesian coordinate system, linking algebra and geometry. He died in Stockholm in 1650 while serving as a tutor to Queen Christina of Sweden.