Demon, demons
Archimandrite Nikifor’s Biblical Encyclopedia
— evil spirits that serve the devil and together with him make up the kingdom of darkness, whose head is the devil (Matt. 12:24–29, and elsewhere). References in the Old and New Testaments to the existence of demons are numerous: in the Old Testament it is related that more than once, when the angels of God appeared before the face of God, the devil appeared together with them, and afterward the various calamities are described in detail with which, by God’s permission, the devil tempted the righteous Job (Job 1:6; 2:2 [as given]).
It is also related that when the Spirit of God departed from Saul, an evil spirit from the Lord troubled him (1 Sam. 16:14). In the Book of Wisdom of Solomon it is said that “through envy of the devil came death into the world” (Wisd. 2:24). In the New Testament, besides the designation “demons,” other names are also used for them, namely: evil spirits (Luke 7:21), spirits (Matt. 10:1), spirits of wickedness (Eph. 6:12), angels of the devil (Matt. 25:41), and the angels of the dragon (Rev. 12:7, 9).