The Catholic view on Daimons

In Greek, "Daimon" is the word for spirits of which there are good and wicked Daimons. In Catholicism, Good Daimons are Angels and Evil Daimons are Demons/Devils. The Christian concept of one's holy guardian angel corresponds to the Hellenic concept of the personal daimon, while the kakodaimon of Greek belief is equivalent to our view of fallen spirits (aka demons). In Greece, good daimons were called agathodaimons. Typically, in Catholicism angels are the term for the spirits, and we distinguish them after the fall as good angels or angels and fallen angels as demons.

St. Thomas Aquinas (who was called the “Angelic Doctor” for good reason) states this in his treatise “On Separated Substances”:

"Furthermore, the opinion of the Platonists, who say that certain demons are good and others are evil—as if having been made good or evil by their own free choice—seems to agree with this opinion. Accordingly, Plotinus, proceeding further, says that the souls of men become demons and the lares are made of men if the latter are of good merit; the lemures or larvae, however, if they are of evil merit; and they are called manes if it is uncertain whether they are of good or evil merit, as Augustine sets forth in On the City of God. This opinion agrees with the aforementioned position of the saints in this, that the latter assert some demons to be good and others evil because of good or evil merits, although it is not customary for us to call the good spirits ‘demons’ but rather ‘angels.’"

"Accordingly, Gregory explaining in a certain homily the words of Ezechiel 28:13, Every precious stone was his covering, says that the leader of the evil angels was, in comparison with the other angels, more brilliant than the rest. And in this respect, he seems to agree with those who asserted some demons to be good and others to be evil, according to which demons are called angels. And therefore it is said in Job 4:18: Behold, they who serve him are not steadfast, and in his angels he found wickedness."

- St. Thomas Aquinas, "On Separated Substances", Chap. 20