Who said I think therefore I am which caused him to become a religious reformer?

The phrase "I think, therefore I am" is attributed to the French philosopher René Descartes. While Descartes is primarily known for his contributions to philosophy and mathematics, he did not become a religious reformer; rather, he focused on epistemology and metaphysics. His ideas about doubt and certainty did influence various fields, including theology, but he did not lead a religious reform movement like figures such as Martin Luther.