It seems hard to believe now, but there was a time, specifically in the 13th century, when the works of Aristotle had fallen out of common usage and were unstudied in the universities of Europe. Thanks to the Muslim scholars of Arabia and Spain, who were enamored of Aristotle's natural philosophy [Islam and its relationship with Western thought has really changed since then, eh?], Aristotle was ready for re-discovery when Thomas of Acquin, a Dominican monk of no small intellect, published a series of works re-presenting Aristotelian thought to his contemporaries and matching it with the theological framework of medieval Christianity. [It is helpful to remember, despite what trendy secularists would have one believe, that Christianity created the university model that educates the Western world to this day; not to mention also enabling scientific method to develop.]
As one with degrees in both philosophy and theology, I can testify to the continued influence of Aquinas in both fields. In fact, his popularity in secular philosophy continues to grow. All subsequent Western philosophy is in reaction to Aquinas's works. There is no greater figure in history whose accomplishments so strongly stand in the face of the errant belief that there is, or should be, a separation between theology, philosophy, and science.
Perhaps his most interesting contribution to human thought is through the field of natural theology. In an overly succinct definition, natural theology is the study of God as known not through sudden revelation, but through the application of observation and reason.
I would encourage readers to follow the links for more information. I will leave with this piquant quotation from G.K. Chesterton, the Catholic writer [and creator of the literary detective "Fr. Brown"] as to Aquinas's ecclesial abilities and ambition:
"His experiences included well-attested cases of levitation in ecstasy; and the Blessed Virgin appeared to him, comforting him with the welcome news that he would never be a Bishop."
He died on this day in the year 1274.