No matter which criteria one uses, Thomas Aquinas (1225–1274) would certainly be listed among the most important and influential philosophers and theologians of that thousand-year period that we call the Middle Ages. He was born in the southern part of Italy and began his studies at the newly founded University of Naples. At the age of nineteen, after overcoming the considerable opposition of his parents, he became a monk by joining the Dominican order and continued his theological studies at the University of Paris, where he remained as a professor of theology for a number of years. His fame as a scholar and a philosopher prompted Pope Urban IV to commission him to produce a systematic exposition and defense of Christian doctrines in light of the recently rediscovered Aristotelian philosophical heritage. Employing the rich logical and philosophical apparatus of the great ancient thinkers at the service of the Catholic Church became the focal point of Aquinas’s intellectual efforts.