Aquinas as Utilitarian. Happiness is the end. Summa Theologica 2-1 q.90 article 2: "Whether the law is always something directed to the common good?":

Now the first principle in practical matters, which are the object of the practical reason, is the last end: and the last end of human life is bliss or happiness, as stated above (Q[2], A[7]; Q[3], A[1]). Consequently the law must needs regard principally the relationship to happiness. Moreover, since every part is ordained to the whole, as imperfect to perfect; and since one man is a part of the perfect community, the law must needs regard properly the relationship to universal happiness. Wherefore the Philosopher, in the above definition of legal matters mentions both happiness and the body politic: for he says (Ethic. v, 1) that we call those legal matters "just, which are adapted to produce and preserve happiness and its parts for the body politic": since the state is a perfect community, as he says in Polit. i, 1.