Saint Anselm of Canterbury
Anselm was an Italian born, Benedictine English philosophical theologian. He is best known for his ontological argument for the existence of God, and the satisfaction theory of the Atonement.
His Monologion and Proslogion both deal extensively with his ontological proofs for God's existence, and the hierarchical order of the universe.
Anselm's other works include De concodia, and his four teaching dialogues: De gramatico, De veritate, De libertate arbitrii, and De casu diaboli. All of his works are remarkable in their display a dialectic structure and his attention to proper linguistic usage.