Here's an excerpt from a great interview with Paul Ryan that appears in the National Catholic Register:
Which Catholic thinkers and documents have influenced you?
The magisterium, the Compendium [of the Social Doctrine of the Church], the encyclicals — you know, the social magisterium is basically the encyclicals and papal letters. People try to paste different epistemological views on me, but if you are going to try to tell me what my philosophy is or what my motivating philosopher is, it would be Thomas Aquinas.
I just finished one of George Weigel’s books that I really liked, but instead of saying a particular theologian or writer, I’d say the magisterium itself, the Compendium, my own prayers. And I believe that the founding principles, the Founders, the American idea, created a society that is well within the political expression of Catholic social teaching.