This Dumb Ox taught the whole Church

Because he was big and strong and sometimes slow to speak, Thomas Aquinas's schoolmates called him the Dumb Ox. Not long afterward, he came to be called Doctor (which means "teacher") because he could actually understand complicated things quickly and explain them well.

Which is what he loved to do, preaching often and writing in the course of his lifetime no fewer than eighty-five works of philosophy and theology books that changed the Church and the world. Indeed, in 1320, less than fifty years after Thomas died, Thomas's biographer said that "throughout the entire world Thomas's teachings have spread among the faithful, and the whole Church is instructed by his voice."

Today, the Church Herself calls Saint Thomas Aquinas the Angelic Doctor ("the teacher who is like an angel"): pure, strong, close to God, and truly a messenger of divine light.