In Abrahamic religions, fallen angels are angels who were expelled from heaven. The literal term “fallen angel” appears neither in the Bible nor in other Abrahamic Scriptures but is used to describe angels cast out of heaven or angels who sinned. Such angels often tempt humans to sin.

The idea of fallen angels derived from the Book of Enoch, a Jewish pseudepigraph, or the assumption that the “sons of God” mentioned in Genesis 6:1–4 are angels. In the period immediately preceding the composition of the New Testament, some sects of Judaism, as well as many Christian Church Fathers, identified these same “sons of God” as fallen angels. During the late Second Temple period the Biblical giants were sometimes considered the monstrous offspring of fallen angels and human women.

In such accounts, God sends the Great Deluge to purge the world of these creatures; their bodies are destroyed, yet their peculiar souls survive, henceforth roaming the earth as demons. Rabbinic Judaism and Christian authorities after the third century rejected the Enochian writings and the notion of an illicit union between angels and women producing giants. Christian theology indicates the sins of fallen angels occur before the beginning of human history. Accordingly, fallen angels became identified with those led by Satan in rebellion against God, also equated with demons.

Evidence for the belief in fallen angels among Muslims can be traced back to reports attributed to some of the companions of Muhammad, such as Ibn Abbas (619–687) and Abdullah ibn Masud (594–653). At the same time, some Islamic scholars opposed the assumption of fallen angels by stressing the piety of angels supported by verses of Quran, such as 16:49 and 66:6, although none of these verses declare angels as immune from sin. One of the first opponents of fallen angels was the early and influential Islamic ascetic Hasan of Basra (642–728).

To support the doctrine of infallible angels, he pointed at verses which stressed the piety of angels, while simultaneously reinterpreting verses which might imply acknowledgement of fallen angels. For that reason, he read the term mala’ikah (angels) in reference to Harut and Marut, two possible fallen angels mentioned in 2:102, as malikayn (kings) instead of malā’ikah (angels), depicting them as ordinary men and advocated the belief that Iblis was a jinni and had never been an angel before. The precise degree of angelic fallibility is not clear even among scholars who accepted fallen angels; according to a common assertion, impeccability applies only to the messengers among angels or if they remain angels.

Academic scholars have discussed whether the Quranic jinn are identical to the Biblical fallen angels. Although the different types of spirits in the Quran are sometimes hard to distinguish, the jinn in Islamic traditions seem to differ in their major characteristics from fallen angels.

Luke 10:18 refers to “Satan falling from heaven” and Matthew 25:41 mentions “the Devil and his angels”, who will be thrown into hell. All Synoptic Gospels identify Satan as the leader of demons. Paul the Apostle (c. 5 – c. 64 or 67) states in 1 Corinthians 6:3 that there are angels who will be judged, implying the existence of wicked angels. 2 Peter 2:4 and Jude 1:6 refer paraenetically to angels who have sinned against God and await punishment on Judgement Day.

The Book of Revelation, chapter 12, speaks of Satan as a great red dragon whose “tail swept a third part of the stars of heaven and cast them to the earth”. In verses 7–9, Satan is defeated in the War in Heaven against Michael and his angels: “the great dragon was thrown down, that ancient serpent who is called the Devil and Satan, the deceiver of the whole world—he was thrown down to the earth and his angels were thrown down with him”. Nowhere within the New Testament writings are fallen angels identified with demons, but by combining the references to Satan, demons and angels, early Christian exegetes equated fallen angels with demons, for which Satan was regarded as the leader.

Origen and other Christian writers linked the fallen morning star of Isaiah 14:12 of the Old Testament to Jesus’ statement in Luke 10:18 that he “saw Satan fall like lightning from heaven”, as well as a passage about the fall of Satan in Revelation 12:8–9. The Latin word lucifer, as introduced in the late 4th-century AD Vulgate, gave rise to the name for a fallen angel.

Christian tradition has associated Satan not only with the image of the morning star in Isaiah 14:12, but also with the denouncing in Ezekiel 28:11–19 of the king of Tyre, who is spoken of as having been a “cherub”. The Church Fathers saw these two passages as in some ways parallel, an interpretation also testified in apocryphal and pseudepigraphic works. However, “no modern evangelical commentary on Isaiah or Ezekiel sees Isaiah 14 or Ezekiel 28 as providing information about the fall of Satan”.

During the period immediately before the rise of Christianity, the intercourse between the Watchers and human women was often seen as the first fall of the angels. Christianity stuck to the Enochian writings at least until the third century. Many Church Fathers such as Irenaeus, Justin Martyr, Clement of Alexandria and Lactantius accepted the association of the angelic descent myth to the “sons of God” passage in Genesis 6:1–4. However, some ascetics, such as Origen (c. 184 – c. 253), rejected this interpretation.

According to the Church Fathers who rejected the doctrine by Origen, these angels were guilty of having transgressed the limits of their nature and of desiring to leave their heavenly abode to experience sensual experiences. Irenaeus referred to fallen angels as apostates, who will be punished by an everlasting fire. Justin Martyr (c. 100 – c. 165) identified pagan deities as fallen angels or their demonic offspring in disguise. Justin also held them responsible for Christian persecution during the first centuries. Tertullian and Origen also referred to fallen angels as teachers of astrology.

The Babylonian king, who is described as a fallen “morning star” in Isaiah 14:1–17, was probably the first time identified with a fallen angel by Origen. This description was interpreted typologically both as an angel and a human king. The image of the fallen morning star or angel was thereby applied to Satan by early Christian writers, following the equation of Lucifer to Satan in the pre-Christian century.

By the third century, Christians began to reject the Enochian literature. The sons of God came to be identified merely with righteous men, more precisely with descendants of Seth who had been seduced by women descended from Cain. The cause of evil was shifted from the superior powers of angels to humans themselves, and to the very beginning of history; the expulsion of Satan and his angels on the one hand and the original sin of humans on the other hand. However, the Book of Watchers, which identified the sons of God with fallen angels, was not rejected by Syriac Christians.

 Augustine of Hippo’s work Civitas Dei (5th century) became the major opinion of Western demonology and for the Catholic Church. He rejected the Enochian writings and stated that the sole origin of fallen angels was the rebellion of Satan. As a result, fallen angels came to be equated with demons and depicted as non-sexual spiritual entities. The exact nature of their spiritual bodies became another topic of dispute during the Middle Ages.

 Augustine based his descriptions of demons on his perception of the Greek Daimon. The Daimon was thought to be a spiritual being, composed of ethereal matter, a notion also used for fallen angels by Augustine. However, these angels received their ethereal body only after their fall. Later scholars tried to explain the details of their spiritual nature, asserting that the ethereal body is a mixture of fire and air, but that they are still composed of material elements. Others denied any physical relation to material elements, depicting the fallen angels as purely spiritual entities. But even those who believed the fallen angels had ethereal bodies did not believe that they could produce any offspring.

Augustine, in his Civitas Dei describes two cities (Civitates) distinct from each other and opposed to each other like light and darkness. The earthly city is caused by the act of rebellion of the fallen angels and is inhabited by wicked men and demons (fallen angels) led by Satan. On the other hand, the heavenly city is inhabited by righteous men and the angels led by God. Although, his ontological division into two different kingdoms shows resemblance of Manichean dualism, Augustine differs in regard of the origin and power of evil. In Augustine works, evil originates from free will. Augustine always emphasized the sovereignty of God over the fallen angels.

 Accordingly, the inhabitants of the earthly city can only operate within their God-given framework. The rebellion of angels is also a result of the God-given freedom of choice. The obedient angels are endowed with grace, giving them a deeper understanding of God’s nature and the order of the cosmos. Illuminated by God-given grace, they became incapable of feeling any desire for sin. The other angels, however, are not blessed with grace, thus they remain capable of sin. After these angels decide to sin, they fall from heaven and become demons.

In Augustine’s view of angels, they cannot be guilty of carnal desires since they lack flesh, but they can be guilty of sins that are rooted in spirit and intellect such as pride and envy. However, after they have made their decision to rebel against God, they cannot turn back. The Catechism of the Catholic Church does not take “the fall of the angels” literally, but as a radical and irrevocable rejection of God and his reign by some angels who, though created as good beings, freely chose evil, their sin being unforgivable because of the irrevocable character of their choice, not because of any defect in infinite divine mercy. Present-day Catholicism rejects Apocatastasis, the reconciliation with God suggested by the Church Father Origen.

Like Catholicism, Protestantism continues with the concept of fallen angels as spiritual entities unrelated to flesh, but it rejects the angelology established by Catholicism. Martin Luther’s (1483–1546) sermons of the angels merely recount the exploits of the fallen angels and does not deal with an angelic hierarchy. Satan and his fallen angels are responsible for some misfortune in the world, but Luther always believed that the power of the good angels exceeds those of the fallen ones. The Italian Protestant theologian Girolamo Zanchi (1516–1590) offered further explanations for the reason behind the fall of the angels. According to Zanchi, the angels rebelled when the incarnation of Christ was revealed to them in incomplete form. While Mainline Protestants are much less concerned with the cause of angelic fall, arguing that it is neither useful nor necessary to know, other Protestant churches do have fallen angels as more of a focus.