On a recent reading of St. John Paul II's Veritatis Splendor, I came across the following rather striking passage (from article 38), which quotes Gregory's De Hominis Opificio, Chapter IV.
Taking up the words of Sirach, the Second Vatican Council explains the meaning of that "genuine freedom" which is "an outstanding manifestation of the divine image" in man: "God willed to leave man in the power of his own counsel, so that he would seek his Creator of his own accord and would freely arrive at full and blessed perfection by cleaving to God" (Gaudium et Spes, 17; cf. Sir 15:14). These words indicate the wonderful depth of the sharing in God's dominion to which man has been called: they indicate that man's dominion extends in a certain sense over man himself. This has been a constantly recurring theme in theological reflection on human freedom, which is described as a form of kingship. For example, Saint Gregory of Nyssa writes: "The soul shows its royal and exalted character... in that it is free and self-governed, swayed autonomously by its own will. Of whom else can this be said, save a king?... Thus human nature, created to rule other creatures, was by its likeness to the King of the universe made as it were a living image, partaking with the Archetype both in dignity and in name."
Today's image, a 14th century fresco of St. Gregory of Nyssa in Chora Church, Istanbul, comes from Wikipedia.