Saint Thomas Aquinas, O.P. (also Thomas of Aquin or Aquino; c. 1225 – 7 March 1274) was an ItalianCatholic priest in the Dominican Order, a philosopher and theologian in the scholastic tradition, known as Doctor Angelicus, Doctor Universalis and Doctor Communis. He was the foremost classical proponent of natural theology, and the father of the Thomistic school of philosophy and theology.
One of the core values espoused by Thomas Aquinas was the belief that scientific inquiry and religious inquiry were compatible. In an alternate where some seventy years after Aquinas' death the Great Black Deaths killed 80% of the population of Europe, Christianity went through a major change when a French man named Henri was first executed and then recognized as the Second Son of God.
While Henri's views on scientific inquiry were far less hostile than the Islam's, it did not embrace Aquinas' view. Thus a Scientific Revolution never took place, ensuring that the alternate's technology remained far behind that of the home timeline.