Thomas Aquinas (1225-1274), Italian Dominican Priest. He is considered to be amongst the most important Medieval theologians and philosophers. His work on Scholasticism, the attempt to reconcile Christianity with Aristotelian philosophy, greatly influenced Catholic thinking and thus Western thought, particulary in ethics, natural law and political theory. His doctrinal system is known as Thomism. Major works are the Summa Theologiae and the Summa Contra Gentiles.