Sauron (pronounced [ˈsaʊrɔn]) is the title character and the primary antagonist, through the forging of the One Ring, of J. R. R. Tolkien's The Lord of the Rings, where he rules the land of Mordor and has the ambition of ruling the whole of Middle-earth. In the same work, he is identified as the "Necromancer" of Tolkien's earlier novel The Hobbit. The Silmarillion describes him as the chief lieutenant of the first Dark Lord, Morgoth. Tolkien noted that the Ainur, the "angelic" powers of his constructed myth, "were capable of many degrees of error and failing", but by far the worst was "the absolute Satanic rebellion and evil of Morgoth and his satellite Sauron". Sauron appears most often as "the Eye", as if disembodied.

Tolkien, while denying that absolute evil could exist, stated that Sauron came as near to a wholly evil will as was possible. Commentators have compared Sauron to the title character of Bram Stoker's 1897 novel Dracula, and to Balor of the Evil Eye in Irish mythology. Sauron is briefly seen in a humanoid form in Peter Jackson's film trilogy, which otherwise shows him as a disembodied, flaming Eye.

The Ainulindalë explains how the supreme being Eru began the creation with good, immortal, angelic spirits, the Ainur. These were the lesser Maiar including Sauron, and the greater Valar. Sauron perceived Eru directly. He was "far higher" than the Maiar who later came to Middle-earth as Wizards. The Vala Melkor rebelled against Eru, starting the evils which Sauron continued.

Sauron served Aulë, the smith of the Valar, acquiring much knowledge; he was at first called Mairon (Quenya: "The Admirable") until he joined Melkor. In Beleriand, he was called Gorthu ("Mist of Fear") and Gorthaur ("The Cruel") in Sindarin. Sauron was drawn to Melkor's power, as he hated disorder. Sauron became a spy for Melkor on the isle of Almaren, the Valar's home. Melkor soon destroyed Almaren; the Valar moved to Valinor, not perceiving Sauron's treachery. Sauron followed Melkor to Middle-earth, and openly joined the Valar's enemy.

Sauron helped Melkor in every kind of deceit. By the time Elves awoke, Sauron was Melkor's lieutenant with command over the stronghold of Angband. The Valar made war on Melkor and captured him, but Sauron escaped. He hid, repaired Angband, and bred an army of Orcs. Melkor, now called Morgoth, murdered Finwë, King of the Noldor, and escaped to Middle-earth with the Silmarils, pursued by the Noldor. Sauron directed the war against the Elves, conquering their fortress of Minas Tirith (not the later city in Gondor) on the isle of Tol Sirion. Lúthien came there to save her lover, the imprisoned Beren, with Huan the Wolfhound. Sauron, as a werewolf, battled Huan, who took him by the throat; he was defeated and left as a huge vampire bat. Lúthien destroyed the tower and rescued Beren. Eärendil eventually sailed to Valinor, and the Valar moved against Morgoth in the War of Wrath; he was cast into the Outer Void beyond the world, but again Sauron escaped.

About 500 years into the Second Age, Sauron reappeared, intent on taking over Middle-earth. To seduce the Elves into his service, Sauron assumed a fair appearance as Annatar, "Lord of Gifts" and befriended Celebrimbor's Elven-smiths of Eregion. He taught them arts and magic, helping them to forge the Rings of Power. Sauron secretly forged the One Ring, to rule all the others, in Mordor's volcanic Mount Doom. The Elves detected his influence when he put on the One Ring, and removed their Rings. Enraged, Sauron made war and overran Eregion, killed Celebrimbor, and seized the Seven and the Nine Rings of Power. The Three Rings were secretly entrusted to the Elves Gil-galad, Círdan, and Galadriel. Sauron attacked them. The Elves were saved by an army from Númenor, defeating Sauron. Sauron fortified Mordor and completed the Dark Tower of Barad-dûr. He distributed the Seven and the Nine Rings to lords of Dwarves and Men. Dwarves would not submit, but he enslaved Men as the feared Nazgûl. Orcs, Trolls, Easterlings and men of Harad became his servants.

Toward the end of the Second Age, Númenor sought to colonize Middle-earth. Led by Ar-Pharazôn, a massive army sailed to Middle-earth to battle Sauron. Dismayed by Númenor's might, Sauron surrendered, hoping to corrupt Númenor from within. With the One Ring, Sauron soon dominated the Númenóreans, undermining Númenor's religion, and inciting the island to worship Melkor with human sacrifice. Sauron convinced Ar-Pharazôn to attack Aman by sea to steal immortality from the Valar. The Valar appealed to Eru, who destroyed Númenor. Sauron's body was destroyed and he lost the ability to appear beautiful.

Led by Elendil, nine ships escaped from the Downfall; they founded the kingdoms of Gondor and Arnor in Middle-earth. Sauron returned to Mordor and made war on these Exiles. He captured Minas Ithil; Elendil's son Isildur escaped down the Anduin. Anárion defended Osgiliath and drove Sauron's forces back to the mountains. Elendil, Isildur and Anárion formed the Last Alliance with the Elves and defeated Sauron at Dagorlad. They invaded Mordor and besieged Barad-dûr for seven years. Finally, Sauron came out to fight face-to-face, killing Elendil and Gil-galad; Elendil's sword Narsil broke beneath him. Isildur took up the hilt-shard and cut the One Ring from Sauron's hand, vanquishing Sauron. Isildur refused to destroy the Ring by casting it into Mount Doom, but kept it for his own.

Isildur was ambushed by Orcs at the Gladden Fields. Isildur put on the Ring and attempted to escape by swimming across Anduin, but the Ring slipped from his finger. Isildur was killed by Orc archers. Sauron spent a thousand years as a shapeless evil.

Sauron eventually reembodied. He concealed himself in Mirkwood as the Necromancer, in the stronghold of Dol Guldur, "Hill of Sorcery". The chief of the Nazgûl, the Witch-king of Angmar, destroyed the northern realm of Arnor. When attacked by Gondor, the Witch-king retreated to Mordor. The Nazgûl captured Minas Ithil, renamed Minas Morgul, and seized its palantír, a seeing stone from Númenor. The White Council of Wizards discovered Sauron, and drove him from Mirkwood. He returned to Mordor, openly declared himself, rebuilt Barad-dûr, and bred armies of large orcs, Uruks.

The One Ring, lost in the Anduin, was found by the hobbit Sméagol. The Ring corrupted him. He shunned sunlight and took on the personality of Gollum. He retreated into caves, obsessed with the Ring, his "Precious". The Ring slipped from him and was picked up by Bilbo Baggins. Gollum attempted to murder Bilbo and reclaim the Ring, but Bilbo escaped when the Ring slipped onto his finger. Many years later, Gandalf identified Bilbo's ring, now passed down to his cousin Frodo, as Sauron's One Ring. He tasked Frodo with taking the Ring to Rivendell.

Sauron tortured Gollum and discovered where the Ring was.

Sauron sent the Nazgûl to pursue Frodo, but he escaped to Rivendell, where Elrond convened a council. It determined that the Ring should be destroyed in Mount Doom by the Company of the Ring. Saruman attempted to capture the Ring, but he was defeated. The palantír of Orthanc fell into the hands of the Company; Aragorn, Isildur's descendant and heir to the throne of Gondor, used it to show himself to Sauron as if he held the Ring. Sauron, troubled, attacked Minas Tirith prematurely. His army was destroyed at the Battle of the Pelennor Fields. Frodo entered Mordor through the pass of Cirith Ungol. Aragorn diverted Sauron's attention with an attack on the Black Gate of Mordor. Frodo reached Mount Doom, but claimed the Ring for himself, revealing the Ring to Sauron. Gollum seized the Ring and fell into the Cracks of Doom, destroying it and himself. Sauron was utterly defeated, and vanished from Middle-earth.

Tolkien never described Sauron's appearance in detail, though he painted a watercolour illustration of him. Sarah Crown, in The Guardian, wrote that "we're never ushered into his presence; we don't hear him speak. All we see is his influence". She called it "a bold move, to leave the book's central evil so undefined – an edgeless darkness given shape only through the actions of its subordinates", with the result that he becomes "truly unforgettable ... vaster, bolder and more terrifying through his absence than he could ever have been through his presence".

He was initially able to change his appearance at will, but when he became Morgoth's servant, he took a sinister shape. In the First Age, the outlaw Gorlim was ensnared and brought into "the dreadful presence of Sauron", who had daunting eyes. In the battle with Huan, the hound of Valinor, Sauron took the form of a werewolf. Then he assumed a serpent-like form, and finally changed back "from monster to his own accustomed [human-like] form". He took on a beautiful appearance at the end of the First Age to charm Eönwë, near the beginning of the Second Age when appearing as Annatar to the Elves, and again near the end of the Second Age to corrupt the men of Númenor. He appeared then "as a man, or one in man's shape, but greater than any even of the race of Númenor in stature ... And it seemed to men that Sauron was great, though they feared the light of his eyes. To many he appeared fair, to others terrible; but to some evil." After the destruction of his fair form in the fall of Númenor, Sauron always took the shape of a terrible dark lord. His first incarnation after the Downfall of Númenor was hideous, "an image of malice and hatred made visible". Isildur recorded that Sauron's hand "was black, and yet burned like fire".

Throughout The Lord of the Rings, "the Eye" (known by other names, including the Red Eye, the Evil Eye, the Lidless Eye, the Great Eye) is the image most often associated with Sauron. Sauron's Orcs bore the symbol of the Eye on their helmets and shields, and referred to him as the "Eye" because he did not allow his name to be written or spoken, according to Aragorn. The Lord of the Nazgûl threatened Éowyn with torture before the "Lidless Eye" at the Battle of the Pelennor Fields. Frodo had a vision of the Eye in the Mirror of Galadriel:

The Eye was rimmed with fire, but was itself glazed, yellow as a cat's, watchful and intent, and the black slit of its pupil opened on a pit, a window into nothing.

Later, Tolkien writes as if Frodo and Sam really glimpse the Eye directly. The mists surrounding Barad-dûr are briefly withdrawn, and:

one moment only it stared out ... as from some great window immeasurably high there stabbed northward a flame of red, the flicker of a piercing Eye ... The Eye was not turned on them, it was gazing north ... but Frodo at that dreadful glimpse fell as one stricken mortally.

This raises the question of whether an "Eye" was Sauron's actual manifestation, or whether he had a body beyond the Eye. Gollum (who was tortured by Sauron in person) tells Frodo that Sauron has, at least, a "Black Hand" with four fingers. The missing finger was cut off when Isildur took the Ring, and the finger was still missing when Sauron reappeared centuries later. Tolkien writes in The Silmarillion that "the Eye of Sauron the Terrible few could endure" even before his body was lost in the War of the Last Alliance. In the draft text of the climactic moments of The Lord of the Rings, "the Eye" stands for Sauron's very person, with emotions and thoughts:

The Dark Lord was suddenly aware of him [Frodo], the Eye piercing all shadows ... Its wrath blazed like a sudden flame and its fear was like a great black smoke, for it knew its deadly peril, the thread upon which hung its doom ... [I]ts thought was now bent with all its overwhelming force upon the Mountain..."

Christopher Tolkien comments: "The passage is notable in showing the degree to which my father had come to identify the Eye of Barad-dûr with the mind and will of Sauron, so that he could speak of 'its wrath, its fear, its thought'. In the second text ... he shifted from 'its' to 'his' as he wrote out the passage anew."

Since the earliest versions of the Silmarillion legendarium, as detailed in the History of Middle-earth series, Sauron underwent many changes. The prototype or precursor Sauron-figure was a giant monstrous cat, the Prince of Cats. Called Tevildo, Tifil and Tiberth among other names, this character played the role later taken by Sauron in the earliest version of the story of Beren and Tinúviel in The Book of Lost Tales in 1917. The Prince of Cats was later replaced by Thû, the Necromancer. The name was then changed to Gorthû, Sûr, and finally to Sauron. Gorthû, in the form Gorthaur, remained in The Silmarillion; both Thû and Sauron name the character in the 1925 Lay of Leithian.

The story of Beren and Lúthien also features the heroic hound Huan and involved the subtext of cats versus dogs in its earliest form. Later the cats were changed to wolves or werewolves, with Sauron becoming the Lord of Werewolves.

Before the 1977 publication of The Silmarillion, Sauron's origins and true identity were unclear to those without access to Tolkien's notes. In 1968, the poet W. H. Auden conjectured that Sauron might have been one of the Valar.

Tolkien stated in his Letters that although he did not think "Absolute Evil" could exist as it would be "Zero", "in my story Sauron represents as near an approach to the wholly evil will as is possible." He explained that, like "all tyrants", Sauron had started out with good intentions but was corrupted by power, and that he "went further than human tyrants in pride and the lust for domination", being in origin an immortal (angelic) spirit. He began as Morgoth's servant; became his representative, in his absence in the Second Age; and at the end of the Third Age actually claimed to be 'Morgoth returned'".

The classicist J. K. Newman comments that "Sauron's Greek name" makes him "the Lizard", from Ancient Greek σαῦρος (sauros) 'lizard or reptile', and that in turn places Frodo (whose quest destroys Sauron) as "a version of Praxiteles' Apollo Sauroktonos", Apollo the Lizard-killer.

Gwenyth Hood, writing in Mythlore, compares Sauron to Count Dracula from Bram Stoker's 1897 novel Dracula. In her view, both of these monstrous antagonists seek to destroy, are linked to powers of darkness, are parasitical on created life, and are undead. Both control others psychologically and have "hypnotic eyes". Control by either of them represents "high spiritual terror" as it is a sort of "damnation-on-earth".

Edward Lense, also writing in Mythlore, identifies a figure from Celtic mythology, Balor of the Evil Eye, as a possible source for the Eye of Sauron. Balor's evil eye, in the middle of his forehead, was able to overcome a whole army. He was a leader of the supernatural Fomorians. Lense further compares Mordor to "a Celtic hell", just as the Undying Lands of Aman resemble the Celtic Earthly Paradise of Tír na nÓg in the furthest (Atlantic) West; and Balor "ruled the dead from a tower of glass".

The Tolkien scholar Verlyn Flieger writes that if there was an opposite to Sauron in The Lord of the Rings, it would not be Aragorn, his political opponent, nor Gandalf, his spiritual enemy, but Tom Bombadil, the earthly Master who is entirely free of the desire to dominate and hence cannot be dominated.

Sauron's opposite, as analysed by Verlyn Flieger

	Sauron	Tom Bombadil
Role	Antagonist	Earthly counterpart
Title	Dark Lord	"Master"
Purpose	Domination of whole of Middle-earth	Care for The Old Forest "No hidden agenda, no covert desire or plan of operation"
Effect of the One Ring	"Power over other wills"	No effect on him "as he is not human", nor does it make others invisible to him, or him to others
How he sees the Ring	Means of domination	Looks right through it, his "blue eye peering through the circle of the Ring"

In film versions of The Lord of the Rings, Sauron has been left off-screen as "an invisible and unvisualizable antagonist" as in Ralph Bakshi's 1978 animated version, or as a disembodied Eye, as in Rankin/Bass's 1980 animated adaptation of The Return of the King.

In the 2001–2003 film trilogy directed by Peter Jackson, Sauron is voiced by Alan Howard. He is briefly shown as a large humanoid figure clad in spiky black armour, portrayed by Sala Baker, but appears only as the disembodied Eye throughout the rest of the storyline. In earlier versions of Jackson's script, Sauron does battle with Aragorn, as shown in the extended DVD version of The Lord of the Rings: The Return of the King. The scene was removed as too large a departure from Tolkien's text and was replaced with Aragorn fighting a troll. Sauron appears as the Necromancer in Jackson's The Hobbit film adaptations, where he is voiced by Benedict Cumberbatch.

Sauron appears in the form of his eye in the 2017 The Lego Batman Movie voiced by Jemaine Clement. He is one of the many classic villains the Joker frees from the Phantom Zone to run amok in Gotham City.

Sauron appears in the merchandise of the Jackson films, including computer and video games. These include The Lord of the Rings: The Battle for Middle-earth II (where he was voiced by Fred Tatasciore), The Lord of the Rings: Tactics, and The Lord of the Rings: The Third Age. In the Lord of the Rings Online game, he is featured as an enemy.

Sauron's rise to power in the Second Age is portrayed in the Amazon prequel series The Lord of the Rings: The Rings of Power. He first appears disguised as the non-canonical human character Halbrand, and then in the second season as Annatar (a canonical alias of Sauron), both played by Charlie Vickers. The Halbrand persona was conceived to make the audience share the feeling of being deceived by Sauron, and to ensure he would not overshadow other characters. Afterwards, he would be allowed to function like other classic TV villains (such as Walter White or Tony Soprano), or Lucifer in John Milton's Paradise Lost. Vickers said he was unaware of his character's true identity until filming the third episode. He admitted he began to suspect when lines from John Milton's Paradise Lost, a narrative poem about the biblical story of the fall of man, were used during an audition. Jack Lowden portrays the character's First Age and early Second Age form in flashback in the second season premiere. The depiction of evil in Arda as embodied in Sauron shifts both in Tolkien's writings and in the Amazon series. The prequel adopts Tolkien's use of both Augustinian and Manichean attitudes to evil.

The Eye of Sauron is mentioned in The Stand, a 1978 post-apocalyptic novel written by Stephen King. The villain Randall Flagg possesses an astral body in the form of an "Eye" akin to the Lidless Eye. The novel itself was conceived by King as a "fantasy epic like The Lord of the Rings, only with an American setting". The idea of Sauron as a sleepless eye that watches and seeks the protagonists also influenced King's epic fantasy series The Dark Tower; its villain, the Crimson King, is a similarly disembodied evil presence whose icon is also an eye.

In the Marvel Comics Universe, the supervillain Sauron, an enemy of the X-Men created in 1969, names himself after the Tolkien character. In the comic series Fables, by Bill Willingham, one character is called "The Adversary", an ambiguous figure of immense evil and power believed to be responsible for much of the misfortune in the Fables' overall history. Willingham has stated "The Adversary", in name and in character, was inspired by Sauron.

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