St. Thomas is responsible for the synthesis of the Philosophy of Aristotle with Christian Theology in the 13th Century. The philosophical system he developed came to be known as Thomism.
In Natural Religion (Philosophy of Religion), St. Thomas is best known for his Five Ways of Proving God’s Existence (or the Cosmological Argument for God’s Existence). These five arguments are commonly known as follows:
Read more about St Thomas.
Read a more detailed analysis of Thomas’ work from the Internet Encyclopedia of Philosophy.