AP: There is an important and obscure text in Genesis that plays a crucial role in explaining the origin of evil spirits: Genesis 6:1-4. That text says that the "sons of God" (i.e., angels appointed by God to monitor the land and, according to the Hebrews, were wandering in the first heaven (Book of Enoch) fixed their eyes on the daughters of men, fell in love with them, and from their carnal relationship were born giants of immense stature, "heroes from men of renown" (Gen. 6:4).
This myth seems to be similar to the one in Greek mythology that explains the origin of certain giants: semi-divine and strong beings who were born of the union of gods with women. The biblical text of Genesis says nothing directly of "demons," but we can immediately see how the apocryphal literature of the Old Testament (4th century B.C. to 1st century A.D.) later amplified all this and used it to explain the origin of evil spirits.
Suddenly, around the year 150 or 160 B.C. in the book of Tobit, which belongs to the group of "deuterocanonical" writings (so called because the Jews and Protestants did not allow them in the canon, but the Catholics did), probably originally written in Greek, a demon appears with all their characteristics. This is the famous Asmodeus.
This term is probably taken from the Persian Pantheon: Asmodeus is the Daeva Aesma, one of the seven evil spirits that accompanied Angra Mainyu, Ahriman, his commanding officer. This demon was in love with Sarah, the daughter of Raguel, a relative of Tobias. To keep anyone from touching her, the jealous demon killed seven successive husbands who were brought into the marriage bed on their wedding night.
Tobias, the hero of the story, literally smokes the demon out using an offering. Thanks to the magic smoke produced by burning the heart and liver of a mysterious fish, along with the help of an angel who accompanies him on the Tigris River, the devil fled. The angel Rafael went after the demon in trapped him in Egypt, placing it in chains and rendering it helpless. Tobias, then, could marry Sarah.
In another late Old Testament book, Wisdom 2:24, there is a text that clearly identifies the serpent of paradise with Satan (Greek, the Devil), an identification which has lots of success in the future.
And finally, the same association is made in an apocryphal writing known as the Life of Adam and Eve (also called the Apocalypse of Moses). Referring to the fall of Adam the author of the Book of Wisdom says: "but through the devil's envy death entered the world, and those who belong to his party experience it" (Wisdom 2:24).
Here Satan appears not only as a true opponent of God, but as an adversary and enemy of mankind. In addition, that which is most feared by evil men, namely death, does not come from God, but Satan. The author attributes to him this pernicious evil. And it begins to be drawn the more precise features that later turn into the incarnation of Evil, and a theology starts (more properly a "theodicy") that aims to relieve the divinity of his responsibility in the origin of evil.