The Devil

The Devil, also known as Satan, Lucifer, Iblis, Beelzebub, or the Horned Beast, was the legendary ruler of Hell and its armies of demons, allegedly a fallen angel and an embodiment of absolute evil. There were many conceptions of the Devil in human culture across the millennia. Although some accounts suggested Satan might be a real entity, others showed the human legends of the Devil as deriving from misunderstandings of the natures of distinct entities.

The Doctor was generally skeptical of the Devil without ruling out his existence entirely, sometimes acknowledging other beings they encountered as having a claim to being "the Devil". The Fourth Doctor thought that "Satan" was one of the names of Sutekh, (TV: Pyramids of Mars) and the Tenth Doctor, though initially skeptical of the Beast's claim of being the "true" Devil (rather than simply an entity which happened to have inspired the image of "the Horned Beast"), (TV: The Satan Pit) later repeated the claim to Donna Noble with no apparent doubt, claiming to have indeed met the Devil. (TV: Planet of the Ood) In contrast, the Thirteenth Doctor once stated that she "wasn't a big believer in Satan" while deriding and denouncing King James I's paranoid belief that Satan was "all around us" and the root of all evil. (TV: The Witchfinders)

Additionally, when humans who had witnessed possessing a man asked if it had been "the Devil", the Eighth Doctor even replied that "you could say that"; (PROSE: Prologue) as presented in fictionalised writings by William Shakespeare,  himself once compared himself to Lucifer and the Doctor to Gabriel. (PROSE: Master Faustus)

Whatever his true nature, Satan was the "Prince of Darkness" and a "Master of All Evil", though the titles were not exclusive to him. (PROSE: The Last Few Pages, Deadly Reunion) In addition to the title of "Prince of Darkness", Lucifer was also described as the Lord of Misrule. (PROSE: Deadly Reunion)

Nature and attributes
Toby Zed described his conception of the Devil as an incarnation of "fury and rage and death". (TV: The Satan Pit) Oswald Danes once joked that, should the Devil walk the Earth, he'd certainly work in PR. (TV: Rendition) Saint Michael was Lucifer's traditional enemy, according to Matthew Stobbold, (PROSE: The Burning) although in Master Faustus it was Gabriel whom  evoked as Lucifer's eternal nemesis. (PROSE: Master Faustus)

Satan was traditionally described as having a forked tail. (PROSE: Goth Opera) When adopting a "Devil-form" based on the medieval traditions about Lucifer's appearance, Hades stood as a huge creature with pitch-black skin, sporting a "great horned head" with "burning yellow eyes" and "savage" fangs. He also had clawed hands and feet, and "great leathery wings folded about" his massive body. (PROSE: Deadly Reunion)

The Devil was often thought of by humans as the ruler of Hell and its armies, Winston Churchill once stated that "if Hitler invaded Hell, [he] would give a favourable reference to the Devil", (TV: Victory of the Daleks) and when hearing the Eleventh Doctor hear about "Dark Forces", Amy Pond asked him, half-jokingly, if he was referring to "Lucifer and the armies of Hell". The Doctor answered that he hoped that wasn't it, as, indeed, it wasn't, though he seemed to think of this as possible. (PROSE: The Coming of the Terraphiles)

Supposed history
In footnotes to some lost writing of William Shakespeare's intended for his play Julius Caesar, the Sixth Doctor guessed that some of Shakespeare's images were comparing the fall of Rome to "the War in Heaven between the Angel which culminated in Lucifer being thrown burning down to Hell", with the Eternal City now "forever denied" to the now-fallen angel. (PROSE: Academic Notes) In possibly fictionalised events related in verse by Shakespeare himself in his unfinished play Master Faustus, also referenced Lucifer and Gabriel, describing himself. and the Doctor as "falling in endless fight like Lucifer and Gabriel". (PROSE: Master Faustus)

According to the Bible, Jesus Christ once met Satan in a desert. (PROSE: Goth Opera)

According to legend, in the Czech Republic in the 13th century, a monk made a bargain with the Devil to be able to transcribe t"he entirety of the Holy Bible, as well as several other historical texts" in one night. The Devil, "trickster that he was", had a portrait of himself included in the book as a condition of the agreement. The book was subsequently known as "the Devil’s Bible". Erasmus Greatorex, however, held that the "Master of All Evil" that the monk had summoned was not Satan but another "demon straight from Hell", an "Ancient". The Preternatural Research Bureau discovered as much, finding out that the entity's name began with YSSG–. (PROSE: The Last Few Pages)

Alleged origins of the myth
Many accounts suggested that the Devil as commonly understood was not quite real, but the legends and image were rooted in true phenomena, although these accounts disagreed as to their nature.

The Beast
The Beast was a demonic entity imprisoned at the centre of the planet Krop Tor at the Dawn of Time by the Disciples of the Light, who claimed to be older than the universe. The Beast's physical form was a red-skinned titan with a skull-like face, glowing yellow eyes, and horns, but he also had the ability to project his mind out of his body and possess other beings. (TV: The Satan Pit) While under the Beast's psychic control, a chorus of Ood explained that he had "woven himself in the fabric of [mortals'] life since the end dawn of time" and that "Abaddon", "Kroptor", "Satan" and "Lucifer" were all names that referred to him. (TV: The Impossible Planet)

Confronting the Beast, the Doctor asked the Beast "which Devil" he claimed to be, to which he answered "all of them". The Beast claimed to be "the truth behind the myth" of all the Devils of religions which had such a figure, and indeed, more generally, the inspiration of all horned deities of evil, warfare or death. The Doctor guessed that it was possible that the "idea" of the Devil, emanating from the mind of the Beast, could have implanted itself into "the back of every sentient being's minds", and debated with himself whether this truly made the Beast "the real Devil" even if it was true, failing to come to a final conclusion on the matter. (TV: The Satan Pit) He did eventually refer to the Beast as "the Devil" when recalling the encounter to Donna Noble. (TV: Planet of the Ood)

Other
The Dæmons, a powerful horned race from the planet Dæmos, whose technology mirrored common folk beliefs about the Devil in many ways, were believed by the Third Doctor to be the inspiration for Satan based on their experiments on humanity. He believed that they had also influenced other depictions of horned humanoids in cultures around the world, such as the Egyptian ram-headed god Khnum and one Hindu demon.

When Olive Hawthorne, a witch, witnessed 's rituals to raise Azal, the last surviving Dæmon, from his slumber, she did not question that she had glimpsed the one called "Satan, Lucifer, the Prince of Darkness, Beelzebub, the Horned Beast". Examining a villager who had been killed by Azal's servant Bok, the Doctor guardedly said that the one who killed him "wasn't the Devil. At least, not exactly". (TV: The Dæmons) The Fourth Doctor later recalled how the appearance of the Devil figure on Earth was inspired by an alien species conducting a survey mission on the planet. He reflected on this disdainfully, citing it as an example of cultural appropriation. (PROSE: Scratchman)

However, the Fourth Doctor also stated, to Sutekh's own face, that "Satan" had been one of the past names given to Sutekh himself, an Osirian deity who reveled in death and destruction. (TV: Pyramids of Mars)

When humans witnessed attempting to possessing a man, and guessed that the entity was "the Devil", the Eighth Doctor found this a fitting description. (PROSE: Prologue)

Religion and folklore
According to the Tenth Doctor, "more religions than there are planets in the sky" had devils, also known as beasts, including the Arkiphets, Quoldonity, Christianity, Pash Pash, New Judaism, San Klah and the Church of the Tin Vagabond. Neoclassic Congregational didn't have a devil per se, only "the things that men do", which the Doctor claimed was the "same thing in the end". (TV: The Satan Pit)

An encounter between Jesus Christ and Satan in a desert was described in the Bible, although it was sometimes supposed that this was a metaphor for him having been met with "doubt and hunger and thirst" there. (PROSE: Goth Opera)

In the early 17th century, witch hunts sought to find and punish alleged witches who were thought to be "in league with Satan" as he, himself, as an invisible malignant presence, plagued the English countryside by "blighting crops, bewitching animals, plagueing people with fits, sickness and visions". (TV: The Witchfinders)

On Earth, in the 20th and 21st centuries, Satanists worshipped the Devil. (PROSE: Preternatural Days) Victor Lang believed that although these cults followed "their own religious doctrines, usually nonsense that they've invented themselves", they still attracted the attention of the actual Lucifer. After his experience meeting vampires, Lang realised that most Satanic cults which made contact with supernatural powers were actually in contact with vampires who took advantage of their sacrifices and ceremonies to get their supply of blood. (PROSE: Goth Opera)

In works of fiction
In Master Faustus, a play begun but left unfinished by William Shakespeare and which appeared to be based on real events involving and Daleks, "Magister" made reference to Lucifer's fall, comparing it to his own nature as a renegade Lord Temporal. (PROSE: Master Faustus) The Sixth Doctor also believed that a cut passage in Shakespeare's Julius Caesar was trying to parallel the supernatural storm presaging Caesar's death with the events of the War in Heaven, including the fall of Lucifer, although the Doctor missed a key insight about the poem, unable to recognise the ways in which it seemed to be a prophecy of the Fall of Gallifrey, making his entire analysis of Shakespeare's authorial intent ssomewhat uspect. (PROSE: Academic Notes)

Lucifer was a character in Faust. Although he was only on-stage for about ten minutes, Ilmatar, who played the character in a production with the European Contemporary Opera Company, was featured prominently on the poster and had a whole page in The Echo. (AUDIO: Dinner and a Show)

Inside the bottle universe to which Christine Summerfield was native, the movie Rosemary's Baby featured some murderous "Satan-worshippers". There also existed a Quatermass movie where "the Devil turned out to be a Martian and tore up half of London at the end". (PROSE: Dead Romance)

Misidentifications
When Momus stole Joan of Arc from Earth, she believed it was a trick of the Devil. (PROSE: The Lonely Computer)

In 1140, the Krillitane in Worcester were thought to be the Devil. (PROSE: The Krillitane Storm)

In the 17th century she became possessed by a fragment of the liquified Morax, Becka Savage believed herself to bear the "mark of Satan" and began a witch hunt. This eventually drew the attention of King James I; press-ganged by the Thirteenth Doctor and her "Fam" into helping reseal the Morax into the hill from which they'd escaped, the King continued to interpret the powerful alien beings as a manifestation of Satan, and proudly walked away from the adventure under the unshakable belief that he had indeed "vanquished Satan" despite the Doctor's attempts to explain the truth to him. (TV: The Witchfinders)

The Eighth Doctor helped Matthew Stobbold defeat a fire elemental in the 19th century; Stobbold, and at one stage even the Doctor, though the entity might be the Devil or another demon, before discovering its true nature. (PROSE: The Burning)

In 1928, when Angelo Colasanto learned of Jack Harkness' immortality, he thought he was the Devil. Jack was captured and killed repeatedly, though some thought he was a miracle instead of the Devil. (TV: Immortal Sins)

In 1930, a Hooverville resident called a Dalek that appeared above the settlement "a Devil in the sky". (TV: Evolution of the Daleks)

When Fitzroy contacted Bryn Williams and tried to make a deal with him in 2009, Bryn assumed it was the Devil. (AUDIO: The Devil and Miss Carew)

In his speech to the Clerics in which he told them that the Eleventh Doctor was a living breathing man, Colonel Manton said that the Doctor was not, among other things, the Devil. (TV: A Good Man Goes to War)

Impersonations
In 1588, the Vituperon posed as the Devil. (AUDIO: The Devil's Armada)

During an invasion of New York City in the 21st century, a Cerebravore used Hector's fear of the Devil against him. Hector believed that the Devil came for him because he knew his "sins". (COMIC: Revolutions of Terror)

When first meeting the Third Doctor, the Immortal Hades, the Greeks' Lord of the Underworld, noted that the Doctor did not seem impressed, thinking that he did not look worthy of the title of Princess of Darkness. In an attempt to cow the Doctor, Hades briefly shifted into the appearance of "the Devil of medieval tradition", before returning to his less imposing human-like form to continue the conversation. This did not scare the Doctor either, however. (PROSE: Deadly Reunion)

Scratchman, a being who fed off of entire universes, liked to present himself as the Devil, as he would often reach outside of his own universe to make Faustian bargains with the denizens of another universe. (PROSE: Scratchman)