Summa Theologica book I - II 

Since, as Damascene states (De Fide Orth. ii, 12), man is said to be made in God's image, in so far as the image implies "an intelligent being endowed with free-will and self-movement": now that we have treated of the exemplar, i.e. God, and of those things which came forth from the power of God in accordance with His will; it remains for us to treat of His image, i.e. man, inasmuch as he too is the principle of his actions, as having free-will and control of his actions.