Who blended Christianty with the philosophy of Aristotle delineating the boundary between philosophy and theology?

The most famous theologian to try to reconcile the teachings of Aristotle with the doctrines of the church was St. Thomas Aquinas. Aristotle's writings greatly influenced Aquinas in many aspects of his theological beliefs; Aquinas' idea of the wholly simple timeless God, for example is clearly influenced by Aristotle's theory of the Unmoved Mover. And Aquinas also uses Aristotle's ideas of the Efficient and Final Causes as a basis for his system of Natural Law, upon which many Catholic doctrines are based.