The Unmoved Mover possesses certain attributes that can be deduced analytically: immutability, eternality, unicity, immateriality, and so forth. However, what about the goodness of the Unmoved Mover? Can we infer that God, the Unmoved Mover, is truly good?
Thomas Aquinas provides several arguments that the Unmoved Mover is not only good, but is goodness itself. For now, let's just consider one argument. Thomas writes:
"Again, it was shown above that there is a certain first unmoved mover, namely, God. This mover moves as a completely unmoved mover, which is as something desired. Therefore, since God is the first unmoved mover, He is the first desired. But something is desired in two ways, namely, either because it is good or because it appears to be good. The first desired is what is good, since the apparent good does not move through itself but according as it has a certain appearance of the good, whereas the good moves through itself. The first desired, therefore, God, is truly good." (Summa Contra Gentiles: Book One, ch. 37)
In order to properly understand this passage, we have to keep in mind that a thing can move another in one of two ways. Either X moves Y insofar as X actualizes some potentiality within itself to cause a change in Y, or else X moves Y as an object of desire. An example of the latter is when a person views a beautiful painting. The person is said to be "moved" by the painting, even though the painting itself need not change.
With this in mind, the Unmoved Mover is immutable, and so it can only move things as an object of desire. Yet, to be an object of desire is to be good. Now, the Unmoved Mover is either good through itself or through another. However, it cannot be good through another, since that would entail that the Unmoved Mover has a potentiality actualized by an external cause. Given that the Unmoved Mover is pure actuality, and exemplifies no potentiality, it follows that not only is the Unmoved Mover good, but is goodness itself.