In mainstream Christianity, the devil (or Satan) is a fallen angel who rebelled against God. Satan was expelled from Heaven and sent to Earth. The devil is often identified as the serpent in the Garden of Eden, whose persuasions led to the two corresponding Christian doctrines: the Original Sin and its cure, the Redemption of Jesus Christ. He is also identified as the accuser of Job, the tempter of the Gospels, Leviathan and the dragon in the Book of Revelation.
In Christianity, Satan became the name of the personification of evil. Christian tradition and theology changed Satan from an accuser appointed by God to test men's faith to God's godlike fallen opponent: "the devil". Traditionally, Christians have understood the devil to be the author of lies and promoter of evil. However, the devil can go no further than God allows, resulting in the problem of evil.
Liberal Christianity often views the devil metaphorically. This is true of some Conservative Christian groups too, such as the Christadelphians and the Church of the Blessed Hope. Much of the popular lore of the devil is not biblical; instead, it is a post-medieval Christian reading of the scriptures influenced by medieval and pre-medieval Christian popular mythology.
In the view of many Christians, the devil's first appearance in the Old Testament is as the serpent in the Garden of Eden. The serpent tempts Adam and Eve into eating the fruit of the tree of the knowledge of good and evil, which God had forbidden them to eat, thus causing their expulsion from the Garden and indirectly causing sin to enter the world. In God's rebuke to the serpent, he tells it "And I will put enmity between thee and the woman and between thy seed and her seed; it shall bruise thy head and thou shalt bruise his heel." (Genesis 3:14-15)
Christian scriptures are often interpreted to identify the serpent with the devil. The deuterocanonical Book of Wisdom says, "But by the envy of the devil, death entered the world and they who are in his possession experience it." (Wisdom 2:24) Satan is implicitly identified, in the New Testament, with the serpent in Eden, in Revelation 12:9: "This great dragon — the ancient serpent called the devil, or Satan, the one deceiving the whole world — was thrown down to the earth with all his angels."
Christian teaching about the Satan (Hebrew שָׂטָן, Adversary), to whom God proposes his servant Job is that he appears in the heavenly court to challenge Job, with God's permission. This is one of two Old Testament passages, along with Zechariah 3, where Hebrew ha-Satan (the Adversary) becomes Greek ho diabolos (the Slanderer) in the Greek Septuagint used by the early Christian church. Originally, only the epithet of "the satan" ("the adversary") was used to denote the character in the Hebrew deity's court that later became known as "the devil" (the term "satan" was also used to designate human enemies of the Hebrews that Yahweh raised against them). The article was lost and this title became a proper name: Satan. There is no unambiguous reference to the devil in the Torah, the Prophets, or the Writings.
Zechariah's vision of recently deceased Joshua the High Priest depicts a dispute in the heavenly throne room between Satan and the Angel of the Lord (Zechariah 3:1–2). Goulder (1998) views the vision as related to opposition from Sanballat the Horonite.
Since the time of Origen and Jerome, some Christian concepts of the devil have included the Morning Star in Isaiah 14:12, which is translated Lucifer ("Morning Star" as a noun, "light-bringing" as an adjective) in the Latin Vulgate, and transferred directly from Latin into the King James Version as a name "Lucifer"[a] When the Bible was translated into Latin (the Vulgate), the name Lucifer appeared as a translation of "Morning Star", or the planet Venus, in Isaiah 14:12. Isaiah 14:1-23 is a passage concerned with the plight of Babylon, and its king is referred, in sarcastic and hyperbolic language to as "morning star, son of the dawn". This is because the Babylonian king was considered to be of godly status and of symbolic divine parentage (Bel and Ishtar, associated with the planet Venus).
While this information is available to scholars today via translated Babylonian cuneiform text taken from clay tablets, it was not as readily available at the time of the Latin translation of the Bible. At some point[when?] the reference to "Lucifer" was interpreted as a reference to the moment Satan was thrown from Heaven. And despite the clarity of the chapter as a whole, the 12th verse continues to be put forth as proof that Lucifer was the name of Satan before the fall. Thus Lucifer became another name for Satan and has remained so, owing to popular tradition.
Later, for unknown reasons, Christian demonologists appeared to designate "Satan", "Lucifer", and "Beelzebub" as different entities, each with a different rank in the demonic hierarchy. One hypothesis is that this might have been an attempt to establish a demonic trinity with the same person, akin to the Christian Trinity of Father, Son and the Holy Spirit, but most demonologists do not carry this view.
The cherub in Eden is a figure mentioned in Ezekiel 28:13-14, identified with the King of Tyre, specifically Ithobaal III (reigned 591–573 BCE) who according to Josephus' list of kings of Tyre was reigning contemporary with Ezekiel at the time of the first fall of Jerusalem. Christianity has traditionally linked the reference to the fall of Satan.
The devil figures much more prominently in the New Testament and in Christian theology than in the Old Testament and Judaism. The New Testament records numerous accounts of the devil working against God and his plan. The Temptation of Christ features the devil, and is described in all three synoptic gospels, (Matthew 4:1-11, Mark 1:12-13, and Luke 4:1-13), although in Mark's gospel he is called Satan. In all three synoptic gospels, (Matthew 9:22-29, Mark 3:22-30, and Luke 11:14-20), Jesus' critics accuse him of gaining his power to cast out demons from Beelzebub, the chief demon (often identified with Satan in mainstream Christendom). In response, Jesus says that a house divided against itself will fall, so, logically speaking, why would the devil allow one to defeat the devil's works with his own power?
The New Testament includes numerous instances of demonic possession. Satan himself is said to have entered Judas Iscariot before Judas' betrayal. (Luke 22:3) Jesus encounters those who are possessed and casts out the evil spirit(s). A person may have one demon or multiple demons inhabiting their body. Jesus encountered a man filled with numerous demons in Mark 5:1-20.
The Epistle of Jude makes reference to an incident where the Archangel Michael argued with the devil over the body of Moses. According to the First Epistle of Peter, "Like a roaring lion your adversary the devil prowls around, looking for someone to devour."
According to most Christian eschatology, Satan will wage a final war against Jesus, before being cast into Hell for aeonios.[b] A few early Church Fathers are known to have prayed for Satan's eventual repentance but it was not generally believed that this would happen. On the other hand, Dispensationalists teach that Jesus returns to Earth before the Great Tribulation to reclaim the righteous, dead and living, to meet him in the air (known as the Rapture. Many Fundamentalists believe that immediately following this, the Tribulational period will occur as prophesied in the book of Daniel, while others (especially Seventh-day Adventists) believe that immediately following Jesus' Second Coming, Satan will be bound on this Earth for 1,000 years, after which he will be "loosed for a little season" –this is when the battle of Armageddon (the final confrontation between good and evil) will be waged–and Satan and his followers will be destroyed once and for all, the Earth will be cleansed of all evil and there will be "a new Heaven and a new Earth" where sin will reign no more.
Particularly in the medieval period, Satan was often shown as having horns and a goat's hindquarters (though occasionally with the legs of a chicken or a mule), and with a tail. He was also depicted as carrying a pitchfork, the implement used in Hell to torment the damned, or a trident, deriving from the regalia of the sea-god Poseidon. Occasionally more imaginative depictions were illustrated: sometimes the devil was depicted as having faces all over his body, as in the painting of a Deal with the Devil. Depictions of the devil covered in boils and scars, animal-like hair, and monstrous deformities were also common. None of these images seem to be based on biblical materials, as Satan's physical appearance is never described in the Bible or any other religious text. Rather, this image is apparently based on pagan Horned Gods, such as Pan, Cernunnos, Molek, Selene and Dionysus, common to many pagan religions. Pan in particular looks very much like the images of the medieval Satan. These images later became the basis for Baphomet, which is portrayed in Eliphas Levi's 1854 Dogme et rituel de la haute magie (English translation Transcendental Magic, its Doctrine and Ritual). Even some Satanists use Baphomet as the image of Satan in Satanic worship. It has been alleged that this image was chosen specifically to discredit the Horned God.
What is known of the Cathars largely comes in what is preserved by the critics in the Catholic Church which later destroyed them in the Albigensian Crusade. Alain de Lille, c.1195, accused the Cathars of believing in two gods - one of light, one of darkness. Durand de Huesca, responding to a Cathar tract c.1220 indicates that they regarded the physical world as the creation of Satan. A former Italian Cathar turned Dominican, Sacchoni in 1250 testified to the Inquisition that his former co-religionists believed that the devil made the world and everything in it.
Calvin taught the traditional view of the devil as a fallen angel. Calvin repeats the simile of Saint Augustine: "Man is like a horse, with either God or the devil as rider." In interrogation of Servetus who had said that all creation was part of God, Calvin asked what of the devil? Servetus responded "all things are a part and portion of God".
David Joris was the first of the Anabaptists to venture that the devil was only an allegory (c.1540), his view found a small but persistent following in the Netherlands. The view was transmitted to England and Joris's booklet was reprinted anonymously in English in 1616, prefiguring a spate of non-literal devil interpretations in the 1640s-1660s: Mede, Bauthumley, Hobbes, Muggleton and the private writings of Isaac Newton. In Germany such ideas surfaced later, c.1700, among writers such as Balthasar Bekker and Christian Thomasius.
However the above views remained very much a minority. Daniel Defoe in his The Political History of the Devil (1726) describes such views as a form of "practical atheism". Defoe wrote "that to believe the existence of a God is a debt to nature, and to believe the existence of the Devil is a like debt to reason".
Until John Milton created the character of Satan for his Paradise Lost, the different attributes of Satan were usually ascribed to different entities. The angel who rebelled in Heaven was not the same as the ruler in Hell. The ruler of Hell was often seen as a sort of jailer who never fell from grace. The tempting serpent of Genesis was just a serpent. Milton combined the different parts of the character to show his fall from near-divine beauty and grace to his eventual skulking role as a jealous tempter. He was so successful in his characterization of Satan as a romantic hero who "would rather rule in Hell than serve in Heaven" that his version of Satan has displaced all others.
Against this come the works of writers like Jeffrey Burton Russell, a believer in a literal personal fallen being of some kind. In Lucifer: the Devil in the Middle Ages, the third volume of his five-volume history of the devil, Russell argues that such theologians [as Bultmann, unnamed] are missing that the devil is part and parcel of the New Testament from its origins.
A number of prayers and practices against the devil exist within the Roman Catholic tradition. The Lord's Prayer includes a petition for being delivered from evil, but a number of other specific prayers also exist.
The Prayer to Saint Michael specifically asks for Catholics to be defended "against the wickedness and snares of the devil." Given that some of the Our Lady of Fatima messages have been linked by the Holy See to the "end times", some Catholic authors have concluded that the angel referred to within the Fatima messages is St. Michael the Archangel who defeats the devil in the War in Heaven. Author Timothy Robertson takes the position that the Consecration of Russia was a step in the eventual defeat of Satan by the Archangel Michael.
The process of exorcism is used within the Catholic Church against the devil. The Catechism of the Catholic Church states that: "Jesus performed exorcisms and from him the Church has received the power and office of exorcizing".
"The battle against the devil, which is the principal task of Saint Michael the archangel, is still being fought today, because the devil is still alive and active in the world. The evil that surrounds us today, the disorders that plague our society, man's inconsistency and brokenness, are not only the results of original sin, but also the result of Satan's pervasive and dark action."
Pope Paul VI expressed concern about the influence of the devil and in 1972 stated that: "Satan's smoke has made its way into the Temple of God through some crack". However, Pope John Paul II viewed the defeat of Satan as inevitable.
"The devil is not a myth, but a real person. One must react to the devil, as did Jesus, who replied with the word of God. With the prince of this world one cannot dialogue. Dialogue is necessary among us, it is necessary for peace [...]. Dialogue is born from charity, from love. But with that prince one cannot dialogue; one can only respond with the word of God that defends us."
In Eastern Orthodox Christianity, Satan is one of humanity's three enemies, along with sin and death (in some other forms of Christianity the other two enemies of mankind are "the world", and self (or the flesh), which is to be taken as man's natural tendency to sin).
Evangelicals agree with the Protestant orthodox of theology that Satan is a real, created being given entirely over to evil and that evil is whatever opposes God or is not willed by God. Evangelicals emphasize the power and involvement of Satan in history in varying degrees; some virtually ignore Satan and others revel in speculation about spiritual warfare against that personal power of darkness. 
Some Christian groups and individuals view the devil in Christianity figuratively. They see the devil in the Bible as representing human sin and temptation, and any human system in opposition to God. Early Bible fundamentalist Unitarians and Dissenters like Nathaniel Lardner, Richard Mead, Hugh Farmer, William Ashdowne and John Simpson, and John Epps taught that the miraculous healings of the Bible were real, but that the devil was an allegory, and demons just the medical language of the day. Such views today are taught today by Christadelphians and the Church of the Blessed Hope. Simpson went so far, in his Sermons (publ. posthumously 1816), as to comment that the devil was "really not that bad", a view essentially echoed as recently as 2001 by Gregory Boyd in Satan and the Problem of Evil: Constructing a Trinitarian Warfare Theodicy.
Jehovah's Witnesses believe that Satan was originally a perfect angel who developed feelings of self-importance and craved worship that belonged to God. Satan persuaded Adam and Eve to obey him rather than God, raising the issue—often referred to as a "controversy"—of whether people, having been granted free will, would obey God under both temptation and persecution. The issue is said to be whether God can rightfully claim to be sovereign of the universe. Instead of destroying Satan, God decided to test the loyalty of the rest of humankind and to prove to the rest of creation that Satan was a liar. Jehovah's Witnesses believe that Satan is God's chief adversary and the invisible ruler of the world. They believe that demons were originally angels who rebelled against God and took Satan's side in the controversy.
Jehovah's Witnesses do not believe that Satan lives in Hell or that he has been given responsibility to punish the wicked. Satan and his demons are said to have been cast down from Heaven to Earth in 1914, marking the beginning of the "last days". Witnesses believe that Satan and his demons influence individuals, organizations and nations, and that they are the cause of human suffering. At Armageddon, Satan is to be bound for 1,000 years, and then given a brief opportunity to mislead perfect humanity before being destroyed.
In Mormonism, the devil is a real being, a literal spirit son of God who once had angelic authority, but rebelled and fell prior to the creation of the Earth in a premortal life. At that time, he persuaded a third part of the spirit children of God to rebel with him. This was in opposition to the plan of salvation championed by Jehovah (Jesus Christ). Now the devil tries to persuade mankind into doing evil. Mankind can overcome this through faith in Jesus Christ and obedience to the Gospel.
The Latter-day Saints traditionally regard Lucifer as the pre-mortal name of the devil. Mormon theology teaches that in a heavenly council, Lucifer rebelled against the plan of God the Father and was subsequently cast out. Mormon scripture reads:
"And this we saw also, and bear record, that an angel of God who was in authority in the presence of God, who rebelled against the Only Begotten Son whom the Father loved and who was in the bosom of the Father, was thrust down from the presence of God and the Son, and was called Perdition, for the heavens wept over him—he was Lucifer, a son of the morning. And we beheld, and lo, he is fallen! is fallen, even a son of the morning! And while we were yet in the Spirit, the Lord commanded us that we should write the vision; for we beheld Satan, that old serpent, even the devil, who rebelled against God, and sought to take the kingdom of our God and his Christ—Wherefore, he maketh war with the saints of God, and encompasseth them round about."
After becoming Satan by his fall, Lucifer "goeth up and down, to and fro in the earth, seeking to destroy the souls of men". Mormons consider Isaiah 14:12 to be referring to both the king of the Babylonians and the devil.
Teachings about the devil vary, depending on the local folklore. Still, the characteristics present in the Bible are present in most depictions.
According to the gospels of Matthew (chapter 4), Mark (chapter 1), and Luke (chapter 4), the devil tempted Jesus at the beginning of his ministry. After Jesus fasted forty days and forty nights in the wilderness, the devil approached Jesus with offers of stones turned to bread, rulership over the kingdoms of the Earth (but with subservience to the devil himself), and spectacular protection from physical harm. Satan uses the Scripture of the Old Testament to solidify his arguments. This would indicate Satan's full knowledge of all of Scripture and a use of that knowledge to tempt and deceive man (Mat 4). Jesus refused all three temptations, rebuking Satan with his own knowledge of Scripture (Mat 4).
Christianity holds several different views on Christ's role in defeating Satan. Some emphasize Christ's death and resurrection as sealing Satan's fate, so that the devil is already defeated though not banished. Others emphasize the devil's final judgment when Christ returns, at which time the terror and deceit of Satan will have no more effect on the world. This is because mankind will face final judgment and the earth will be purged or cleansed with fire. Satan will be bound to the lake of fire (Rev 20) with the Beast, the false prophet and all those whose names are not in the Book of Life.
The devil and his demons are portrayed as able to possess and control humans. The Roman Catholic Church occasionally performs exorcisms, usually only after medical and psychological evaluations have taken place to rule out a mental or physical ailment.
The devil has been described as granting magical powers to sorcerers and witches, usually in exchange for worship or souls. In Acts of the Apostles 16:16 Paul the Apostle meets 'a slave girl who had an evil spirit that enabled her to predict the future'. He performs an exorcism using the name of Jesus Christ.
In some Christian traditions, the names Lucifer, Satan, Samael, Beelzebub, Belial are all names for the devil, along with the elliptical expressions the Prince of this World, the Beast and the Dragon, the Serpent or the Old Serpent, the Enemy, the Evil One, the Tempter. Others interpret the names as indicating distinct individuals.
The name Mephistopheles and expressions such as the Prince of Darkness and the Lord of Darkness are treated in the same way.
Epithets include "Old Scratch" and "Old Nick".
Dante, Milton, and several other writers have depicted the devil as resident in Hell. This contrasts with Job 1:6-7 and 1 Peter 5:8, discussed above, which depict the devil as traveling about on the earth. The only point in the Bible where Satan is in a fiery place is at Revelation 20:10 where, at some future time, the devil is thrown into the Lake of Fire and Sulfur to be tormented forever.
"An angel or any other rational creature considered in his own nature, can sin; and to whatever creature it belongs not to sin, such creature has it as a gift of grace, and not from the condition of nature. The reason of this is, because sinning is nothing else than a deviation from that rectitude which an act ought to have; whether we speak of sin in nature, art, or morals. That act alone, the rule of which is the very virtue of the agent, can never fall short of rectitude. Were the craftsman's hand the rule itself engraving, he could not engrave the wood otherwise than rightly; but if the rightness of engraving be judged by another rule, then the engraving may be right or faulty."
medieval devils' weapons...far exceed in variety the stereotypical pitchfork
XVII. Of Predestination and Election