I. (1225–74), Italian philosopher, theologian, and Dominican friar; known as the Angelic Doctor.
He is regarded as the greatest figure of scholasticism; one of his most important achievements was the introduction of the work of Aristotle to Christian western Europe. His works include commentaries on Aristotle as well as the Summa Contra Gentiles, intended as a manual for missionaries, and Summa Theologiae, the greatest achievement of medieval systematic theology. He also devised the official Roman Catholic tenets. Feast day, 28 January.