Background: Saint Thomas Aquinas  (; Italian: Tommaso d'Aquino, lit. 'Thomas of Aquino'; 1225 - 7 March 1274) was an Italian Dominican friar, Catholic priest, and Doctor of the Church. He was an immensely influential philosopher, theologian, and jurist in the tradition of scholasticism, within which he is also known as the Doctor Angelicus and the Doctor Communis.
Context: In 1245 Thomas was sent to study at the Faculty of the Arts at the University of Paris, where he most likely met Dominican scholar Albertus Magnus, then the holder of the Chair of Theology at the College of St. James in Paris. When Albertus was sent by his superiors to teach at the new studium generale at Cologne in 1248, Thomas followed him, declining Pope Innocent IV's offer to appoint him abbot of Monte Cassino as a Dominican. Albertus then appointed the reluctant Thomas magister studentium. Because Thomas was quiet and didn't speak much, some of his fellow students thought he was slow. But Albertus prophetically exclaimed: "You call him the dumb ox, but in his teaching he will one day produce such a bellowing that it will be heard throughout the world." Thomas taught in Cologne as an apprentice professor (baccalaureus biblicus), instructing students on the books of the Old Testament and writing Expositio super Isaiam ad litteram (Literal Commentary on Isaiah), Postilla super Ieremiam (Commentary on Jeremiah) and Postilla super Threnos (Commentary on Lamentations). Then in 1252 he returned to Paris to study for the master's degree in theology. He lectured on the Bible as an apprentice professor, and upon becoming a baccalaureus Sententiarum (bachelor of the Sentences) devoted his final three years of study to commenting on Peter Lombard's Sentences. In the first of his four theological syntheses, Thomas composed a massive commentary on the Sentences titled Scriptum super libros Sententiarium (Commentary on the Sentences). Aside from his masters writings, he wrote De ente et essentia (On Being and Essence) for his fellow Dominicans in Paris. In the spring of 1256 Thomas was appointed regent master in theology at Paris and one of his first works upon assuming this office was Contra impugnantes Dei cultum et religionem (Against Those Who Assail the Worship of God and Religion), defending the mendicant orders, which had come under attack by William of Saint-Amour. During his tenure from 1256 to 1259, Thomas wrote numerous works, including: Questiones disputatae de veritate (Disputed Questions on Truth), a collection of twenty-nine disputed questions on aspects of faith and the human condition prepared for the public university debates he presided over on Lent and Advent; Quaestiones quodlibetales (Quodlibetal Questions), a collection of his responses to questions posed to him by the academic audience; and both Expositio super librum Boethii De trinitate (Commentary on Boethius's De trinitate) and Expositio super librum Boethii De hebdomadibus (Commentary on Boethius's De hebdomadibus), commentaries on the works of 6th-century Roman philosopher Boethius. By the end of his regency, Thomas was working on one of his most famous works, Summa contra Gentiles. CANNOTANSWER
Question: What did he do after this?

Answer:

Thomas taught in Cologne as an apprentice professor (baccalaureus biblicus), instructing students on the books of the Old Testament and writing