Thomas Aquinas was an Italian Dominican friar who taught at the University of Paris. In the Summa Theologica, he united Aristotle's philosophy with Christian faith in a broad, organized system. Canonized and declared a Doctor of the Church, he remains the main philosophical reference of Catholicism today.
Core ideas
Reason and faith do not oppose each other, since both come from God
It is possible to demonstrate the existence of God through five rational ways
There is a natural law, accessible to reason, that guides moral good
The tradition: Scholastic
A Scholastic is a thinker of the medieval universities who used logic and debate to reconcile faith and reason. Thomas Aquinas is the high point of Scholasticism.