Most scholars acknowledge that Judeo-Christianity owes a great debt to Zoroastrianism in regards to the introduction of angelology and demonology, as well as Satan (Ahriman) as the ultimate agent of evil. As the Iranian Avestan and Vedic traditions and also other branches of Indo-European mythologies show, the notion of demon has existed for many centuries.
Ancient Egyptians also believed in demonic like monsters that devoured the human soul, while it traveled towards afterlife, although, certainly demons per se did not exist specifically in pagan Egypt.
The Greek conception of a daemon (δαίμων) appears in the works of Plato and many other ancient authors, but without the evil connotations which are apparent in the Septuagint translation of the Hebrew Bible and in the Greek originals of the New Testament. The medieval and neo-medieval conception of a “demon” in Western civilization (see the Medieval grimoire called the Ars Goetia) derives seamlessly from the ambient popular culture of Late (Roman) Antiquity: Greco-Roman concepts of daemons that passed into Christian culture are discussed in the entry daemon.The Hellenistic “Demon” eventually came to include many Semitic and Near Eastern gods as evaluated by Christianity.
In some present-day cultures, demons are still feared in popular superstition, largely due to their alleged power to possess humans, and they are an important concept in many modern religions and occultist traditions.
In the contemporary Western occultist tradition (perhaps epitomized by the work of Aleister Crowley) a demon, such as Choronzon, the “Demon of the Abyss”, is a useful metaphor for certain inner psychological processes, though some may also regard it as an objectively real phenomenon.
The idea of demons is as old as religion itself, and the word demon seems to have ancient origins. The Merriam-Webster dictionary gives the etymology of the word as Greek daimon, probably from the verb daiesthai meaning “to divide, distribute.” The Proto-Indo-European root *deiwos for god, originally an adjective meaning “celestial” or “bright, shining” has retained this meaning in many related Indo-European languages and cultures (Sanskrit deva, Latin deus, German Tiw), but also provided another other common word for demon in Avestan daeva In modern Greek, the word δαίμων has the same meaning as the modern English demon. But in Ancient Greek, δαίμων meant “spirit” or “higher self”, much like the Latin genius from which comes the word genie.
Demons in the Hebrew Bible
Demons as described in the Tanakh are not the same as “demons” commonly known in popular or Christian culture.
The demons mentioned in the Hebrew Bible are of two classes, the se’irim and the shedim. The se’irim (“hairy beings”), to which some Israelites offered sacrifices in the open fields, are satyr-like creatures, described as dancing in the wilderness (Isaiah xiii. 21, xxxiv. 14), and which are identical with the jinn. (But compare the completely European woodwose.) Possibly to the same class belongs Azazel, the goat-like demon of the wilderness (Leviticus xvi. 10ff), probably the chief of the se’irim, and Lilith (Isaiah xxxiv. 14). Possibly “the roes and hinds of the field”, by which Shulamit conjures the daughters of Jerusalem to bring her back to her lover (Canticles ii. 7, iii. 5), are faunlike spirits similar to the se’irim, though of a harmless nature.
The “stones of the field” (Job v. 23), with which the righteous are said to be in league, seem to be field-demons of the same nature. The wilderness as the home of demons was regarded as the place whence such diseases as leprosy issued, and in cases of leprosy one of the birds set apart to be offered as an expiatory sacrifice was released, that it might carry the disease back to the desert (Leviticus xiv. 7, 52).
The evil spirit that troubled Saul (I Samuel xvi. 14 et seq.) may have been a demon, though the Masoretic text suggests the spirit was sent by God.
Some benevolent shedim were used in kabbalistic ceremonies (as with the golem of Rabbi Yehuda Loevy), and malevolent shedim (mazikin, from the root meaning to wound) are often responsible in instances of possession. Instances of idol worship were often the result of a shed inhabiting an otherwise worthless statue; the shed would pretend to be a God with the power to send pestilence, although such events were not actually under his control.
Influences from Chaldean mythology
In Chaldean mythology the seven evil deities were known as shedu, meaning storm-demons. They were represented in winged bull form, derived from the colossal bulls used as protective genii of royal palaces, the name “shed” assumed also the meaning of a propitious genius in Babylonian magic literature (see Delitzsch, Assyrisches Handwörterbuch. pp. 60, 253, 261, 646; Jensen, Assyr.-Babyl. Mythen und Epen, 1900, p. 453; Archibald Sayce, l.c. pp. 441, 450, 463; Lenormant, l.c. pp. 48-51).
It was from Chaldea that the name “shedu” came to the Israelites, and so the writers of the Tanach applied the word as a dylogism to the Canaanite deities in the two passages quoted. But they also spoke of “the destroyer” (Exodus xii. 23) as a demon whose malignant effect upon the houses of the Israelites was to be warded off by the blood of the paschal sacrifice sprinkled upon the lintel and the door-post (a corresponding pagan talisman is mentioned in Isaiah lvii. 8 ). In II Samuel xxiv; 16 and II Chronicles xxi. 15 the pestilence-dealing demon is called “the destroying angel” (compare “the angel of the Lord” in II Kings xix. 35; Isaiah xxxvii. 36), because, although they are demons, these “evil messengers” (Psalms lxxviii. 49; A. V. “evil angels”) do only the bidding of God; they are the agents of His divine wrath.
There are indications that popular Hebrew mythology ascribed to the demons a certain independence, a malevolent character of their own, because they are believed to come forth, not from the heavenly abode of God, but from the nether world (compare Isaiah xxxviii. 11 with Job xiv. 13; Psalms xvi. 10, xlix. 16, cxxxix. 8 ).
In Jewish rabbinic literature
Rabbinical demonology has three classes of, demons, though they are scarcely separable one from another. There were the shedim, the mazziḳim (“harmers”), and the ruḥin (“evil spirits”). Besides these there were lilin (“night spirits”), ṭelane (“shade”, or “evening spirits”), ṭiharire (“midday spirits”), and ẓafrire (“morning spirits”), as well as the “demons that bring famine” and “such as cause storm and earthquake” (Targ. Yer. to Deuteronomy xxxii. 24 and Numbers vi. 24; Targ. to Cant. iii. 8, iv. 6; Eccl. ii. 5; Ps. xci. 5, 6.)
Hebrew demons were workers of harm. To them were ascribed the various diseases, particularly such as affect the brain and the inner parts. Hence there was a fear of “Shabriri” (lit. “dazzling glare”), the demon of blindness, who rests on uncovered water at night and strikes those with blindness who drink of it (Pesachim 112a; Avodah Zarah 12b); also mentioned were the spirit of catalepsy and the spirit of headache, the demon of epilepsy, and the spirit of nightmare,
These demons were supposed to enter the body and cause the disease while overwhelming or “seizing” the victim (hence “seizure”).. To cure such diseases it was necessary to draw out the evil demons by certain incantations and talismanic performances, in which the Essenes excelled. Josephus, who speaks of demons as “spirits of the wicked which enter into men that are alive and kill them”, but which can be driven out by a certain root (Bellum Judaeorum vii. 6, § 3), witnessed such a performance in the presence of the Emperor Vespasian (“Antiquities” viii. 2, § 5), and ascribed its origin to King Solomon.
The King and Queen of Demons
In some rabbinic sources, the demons were believed to be under the dominion of a king or chief, either Asmodai (Targ. to Eccl. i. 13; Pes. 110a; Yer. Shek. 49b) or, in the older Haggadah, Samael (“the angel of death”), who kills by his deadly poison, and is called “chief of the devils”. Occasionally a demon is called “satan”: “Stand not in the way of an ox when coming from the pasture, for Satan dances between his horns” (Pes. 112b; compare B. Ḳ. 21a).
According to Zoroastrianism, the queen of demons is Lilith, pictured with wings and long flowing hair, and called the “mother of Ahriman” (B. B. 73b; ‘Er. 100b; Nid. 24b). “When Adam, doing penance for his sin, separated from Eve for 130 years, he, by impure desire, caused the earth to be filled with demons, or shedim, lilin, and evil spirits” (Gen. R. xx.; ‘Er. 18b.)
Though the belief in demons was greatly encouraged and enlarged in Babylonia under the influence of the Zoroastrianism that was the religion of the Persian Empire (Parsee) notions, demonology never became an essential feature of Jewish theology. The reality of demons was never questioned by the Talmudists and late rabbis; most accepted their existence as a fact. Nor did most of the medieval thinkers question their reality. Only rationalists like Maimonides and Abraham ibn Ezra, clearly denied their existence. Their point of view eventually became the mainstream Jewish understanding.
In the New Testament and Christianity
“Demon” has a number of meanings, all related to the idea of a spirit that inhabited a place, or that accompanied a person. Whether such a daemon was benevolent or malevolent, the Greek word meant something different from the later medieval notions of ‘demon’, and scholars debate the time in which first century usage by Jews and Christians in its original Greek sense became transformed to the later medieval sense.
In the Gospel of Mark, Jesus casts out many demons, or evil spirits, from those who are afflicted with various ailments (such as epileptic seizures). The imagery is very clear: Jesus is far superior to the power of demons over the human beings that they inhabit, and he is able to free these human victims by commanding and casting out the demons, by binding them, and forbidding them to return.
By way of contrast, in the book of Acts a group of Judaistic exorcists known as the sons of Sceva try to cast out a very powerful spirit without believing in or knowing Jesus , but fail with disastrous consequences. However Jesus himself never fails to vanquish a demon, no matter how powerful (see the account of the demon-possessed man at Gerasim), and even defeats Satan in the wilderness (see Matthew).
There is a description in the Book of Revelation 12:7-17 of a battle between God’s army and Satan’s followers, and their subsequent expulsion from Heaven to earth to persecute humans — although this event is related as being foretold and taking place in the future. In Luke 10:18 it is mentioned that a power granted by Jesus to control demons made Satan “fall like lightning from heaven.”
Augustine of Hippo’s reading of Plotinus, in The City of God (ch.11) is ambiguous as to whether daemons had become ‘demonized’ by the early 5th century:
“He (Plotinus) also states that the blessed are called in Greek eudaimones, because they are good souls, that is to say, good demons, confirming his opinion that the souls of men are demons.”—City of God, ch. 11.—Of the Opinion of the Platonists, that the Souls of Men Become Demons When Disembodied.
If Augustine meant ‘demons’ in the later, medieval sense, the passage would savor of a rhetorical casuistry that is not characteristic of him.
The contemporary Roman Catholic Church unequivocally teaches that angels and demons are real personal beings, not just symbolic devices. The Catholic Church has a cadre of officially sanctioned exorcists which perform many exorcisms each year. The exorcists of the Catholic Church teach that demons attack humans continually but that afflicted persons can be effectively healed and protected either by the formal rite of exorcism, authorized to be performed only by bishops and those they designate, or by prayers of deliverance which any Christian can offer for themselves or others 
In Christian myth and legend
Building upon the few references to daemons in the New Testament, especially the visionary poetry of the Apocalypse of John, Christian writers of apocrypha from the 2nd century onwards created a more complicated tapestry of beliefs about “demons” that was largely independent of Christian scripture.
According to Christian mythology, when God created angels, he offered them the same choice he was to offer humanity: follow, or be cast apart from him. Some angels chose not to follow God, instead choosing the path of evil. These are not the fallen angels, but are the pre-human entities known as demons. The fallen angels are the host of angels who later rebelled against God, headed by Lucifer (who became known as Satan after his rebellion against God). And later the 200 angels known as the Grigori, led by Semyazza, Azazel and other angelic chiefs, some of whom became the demons that were conjured by King Solomon and imprisoned in the brass vessel, the Goetia demons, descended to Earth and cohabited with the daughters of men.
War in Heaven
According to popular tradition, the fall of Satan is portrayed in Ezekiel 28:12-19 and Isaiah 14:12-14. Christian mythology builds upon later Jewish traditions that Satan and his host declared war with God, but that God’s army, commanded by the archangel Michael, defeated the rebels. Their defeat was never in question, since God is by nature omnipotent, but Michael was given the honor of victory in the natural order; thus the rise of Christian veneration of the archangel Michael, beginning at Monte Gargano in 493, reflects the full incorporation of demons into Christianity. God then cast his enemies from Heaven to the abyss, into a newly created prison called Hell (allusions to such a pit are made in the Book of Revelation, as pits of sulphur and fire) where all his enemies should be sentenced to an eternal existence of pain and misery. This pain is not all physical; for their crimes, these angels, now called demons, would be deprived of the sight of God (2 Thessalonians 1:9), this being the worst possible punishment.
An indefinite time later, when God created the earth and humans, Satan and the other demons were allowed to tempt humans or induce them to sin by other means. The first time Satan did this was as a serpent in the earthly paradise or Garden of Eden to tempt Eve, who subsequently drew her husband Adam into her crime. There is a theory that the serpent that tempted Eve was not actually Satan but a minor demon named Cerenus. The theory states that Cerenus made a deal with God to tempt Eve in exchange for liberation from the pit. Due to man’s failure, as part of the punishment, the permission granted to Satan and his demons to tempt the first humans away from their Creator will now last until the end of this age when Christ shall return for the battle of Armageddon. Satan and his host will be confined and Christ shall reign and establish 1000 years of peace upon the earth. At the end of the 1000 years Satan will again be unleashed for a final battle after which the earth shall be renewed by fire.
At various times in Christian history, attempts have been made to classify these beings according to various proposed demonic hierarchies.
According to most Christian demonology demons will be eternally punished and never reconciled with God. Other theories postulate a Universal reconciliation, in which Satan, the fallen angels, and the souls of the dead that were condemned to Hell are reconciled with God. This doctrine is today often associated with the Unification Church. Origen, Jerome and Gregory of Nyssa also mentioned this possibility before it was generally accepted that the fallen state is eternal.
In contemporary Christianity, demons are generally considered to be angels who fell from grace by rebelling against God. Some contest however that this view, championed by Origen, Augustine and John Chrysostom, arose during the 6th century. Another theory that may have preceded or co-existed with the hypothesis of fallen angels was that demons were ostracized from Heaven for the primary sin of mating with mortal women, giving rise to a race of half-human giants known as the Nephilim.
There are still others who say that the sin of the angels was pride and disobedience. It seems quite certain that these were the sins that caused Satan’s downfall (Ezek. 28). If this be the true view then we are to understand the words, “estate” or “principality” in Deuteronomy 32:8 and Jude 6 (“And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.”) as indicating that instead of being satisfied with the dignity once for all assigned to them under the Son of God, they aspired higher.
In pre-Islamic Arab culture
Pre-Islamic mythology does not discriminate between gods and demons. The jinn are considered as divinities of inferior rank, having many human attributes: they eat, drink, and procreate their kind, sometimes in conjunction with human beings; in which latter case the offspring shares the natures of both parents. The jinn smell and lick things, and have a liking for remnants of food. In eating they use the left hand. Usually they haunt waste and deserted places, especially the thickets where wild beasts gather. Cemeteries and dirty places are also favorite abodes. In appearing to man djinn assume sometimes the forms of beasts and sometimes those of men; but they always have some animal characteristic, such as a paw in place of a hand (Darimi, “Kitab al-Sunnah”, ii. 213). Eccentric movements of the dust-whirlwind (“zawabi'”) are taken to be the visible signs of a battle between two clans of jinn.
Generally jinn are peaceable and well disposed toward men. Many a pre-Islamic poet was believed to have been inspired by good jinn; and Muhammad himself was accused by his adversaries of having been inspired by jinn (“majnun”). But there are also evil jinn, who contrive to injure men. Among these are specially conspicuous the three female demons named “Ghulah” (corresponding to the Talmudic Lilith), “Si’lat”, and “‘Aluḳ” or “‘Aulaḳ”, and the four male demons “Afrit”, “Azbab”, “Aziab”, and “Ezb”. Ghulah is especially harmful to new-born children, and in order to keep her away their heads are rubbed with the gum of an acacia.
The word genie, comes from the arabic jinn. This is not surprising considering the story of ala’edin, or the anglisized Aladdin, passed through Arabian merchants enroute to Europe.
In popular culture
In Mikhail Lermontov’s long poem (1840), the Demon makes love to the virgin Tamara in a scenic setting of the Causcaus mountains.
Many classic books and plays feature demons, such as the Divine Comedy, Paradise Lost and Faust.
Anton Rubinstein’s lushly chromatic opera The Demon (1875), based on the poem “The Demon” by Lermontov, was delayed in its production because the censor attached to the Mariinsky Theatre felt that the libretto was sacrilegious . Notably, its aria “Do not weep, child” was used by any bass.
In C. S. Lewis’s The Screwtape Letters a senior demon in Hell’s hierarchy writes a series of letters to his subordinate trainee, Wormwood, offering advice in the techniques of temptation of humans. Though fictional, it offers a plausible contemporary Christian viewpoint of the relationship of humans and demons.
Demons have permeated the culture of children’s animated television series; they are used in comic books as powerful adversaries in the horror, fantasy and superhero stories. There are a handful of demons who fight for good for their own reasons like DC Comics’ The Demon and Marvel Comics’ Ghost Rider.
In Philip Pullman’s His Dark Materials trilogy, dæmons are the physical incarnation of a person’s soul. Although they bear almost no resemblance to Christian demons, the word is pronounced the same.
In recent times, Fr. Gabriele Amorth, chief exorcist at the Vatican, has published two books on his experiences with Satan and demons entitled An Exorcist Tells His Story, and An Exorcist: More Stories published by Ignatius Press.
In the various books of Skeeve and Aahz by Robert Asprin a Demon is short for Dimension Traveller. In world A you would see beings from world B as demons, however, should you leave world A and go to world B, you would be the demon to the locals.
Scientists occasionally invent hypothetical entities with special abilities as part of a thought experiment. These “demons” have abilities that are nearly limitless, but they are still subject to the physical laws being theorized about.
For example, in Descartes’ Second Meditation, it is argued, as a thought experiment, that it is at least possible that there is an all-powerful evil demon who is deceiving me, such that this demon causes me to have false beliefs, including the belief that there is an object before me and the belief that two plus three equals five. Note that the power of such a demon would be two-fold: both empirical and rational thinking can be completely compromised. This leads to a worrisome argument:
1. One knows some fact or other only when one can rule out that there is such a demon.
2. But one can never be in a position rule out that there is such a being, since we can never be sure that the demon isn’t merely toying with our epistemic situation.
3. Thus, we can never know any facts at all!
- Demons in the Catechism of the Catholic Church: Hyperlinked references to demons in the online Catechism of the Catholic Church
- Dictionary of the History of Ideas: Demonology