Two Hobbits, Sméagol and Déagol, are fishing when Déagol discovers the One Ring in the river. Sméagol's mind is ensnared by the Ring, and he kills his friend for it. He retreats into the Misty Mountains as the Ring twists his body and mind until he becomes the creature Gollum.
Centuries later, during the War of the Ring, Gandalf leads Aragorn, Legolas, Gimli, and King Théoden to Isengard, where they reunite with Merry and Pippin. Gandalf retrieves Saruman's palantír, and the group returns to Edoras to celebrate their victory at Helm's Deep. That night, Pippin looks into the palantír and is seen by Sauron. From Pippin's description of his visions, Gandalf surmises that Sauron will attack Gondor's capital Minas Tirith. He rides there to warn Gondor's steward Denethor, taking Pippin with him.
Gollum leads Frodo Baggins and Samwise Gamgee to Minas Morgul, where they watch the Witch-king of Angmar, leader of the nine Nazgûl, lead an army of Orcs towards Gondor. The hobbits begin climbing a stair carved in the cliff face that leads to a secret tunnel into Mordor, unaware that Gollum plans to kill them and take the Ring. The Witch-king and his forces strike and overwhelm Osgiliath, forcing Faramir and his garrison to retreat to Minas Tirith.
Gollum disposes of the Hobbits' food, blaming Sam. Believing that Sam desires the Ring, Frodo tells him to go home before he and Gollum continue to the tunnel leading to Mordor. Gollum tricks him into venturing into the lair of the giant spider Shelob. Frodo narrowly escapes and confronts Gollum, telling him that he must destroy the Ring for both their sakes. Gollum attacks Frodo but falls down a chasm. Frodo continues on, but Shelob discovers, paralyses, and binds him. Sam returns and wounds Shelob, driving her away, but then hides as Orcs appear and take Frodo with them. The Orcs prepare to execute Frodo, but they end up fighting each other over ownership of Frodo's mithril vest; the distraction allows Sam to rescue Frodo, and they escape before going on to continue their journey.
As King Théoden gathers the Rohirrim army, Aragorn learns from Elrond that Arwen is dying, having refused to leave Middle-Earth to be with Aragorn after seeing a vision of their future son. Elrond gives Aragorn Andúril, reforged from the shards of King Elendil's sword Narsil, so that Aragorn can reclaim his birthright and gain reinforcements from the ghostly Dead Men of Dunharrow. Joined by Legolas and Gimli, Aragorn travels to the Dead Men's lair, pledging to release them from Isildur's undead curse should they come to Gondor's aid.
Faramir is gravely wounded after a futile effort to recapture Osgiliath; believing his son to be dead, Denethor falls into madness. Gandalf is left to defend the city against the Orc army, led by Gothmog. As Gothmog's army forces its way into the city, Denethor attempts to kill himself and Faramir on a pyre. Pippin alerts Gandalf and they save Faramir, but a burning Denethor leaps to his death from the top of Minas Tirith just before Théoden and his nephew, Éomer, arrive with the Rohirrim. During the ensuing battle, they are overwhelmed by the Oliphaunt-riding Haradrim and the Witch-King mortally wounds Théoden. Just as the Witch-king prepares to finish Théoden off, his niece Éowyn battles and manages to kill the Witch-king with Merry's help; Éowyn subsequently tends to Théoden afterwards and they bid each farewell before Théoden dies in front of his niece. Aragorn then arrives with the Army of the Dead, who overcome Sauron's forces and win the battle. Aragorn frees the Dead Men from their curse.
Aragorn decides to march upon the Black Gate as a distraction so Frodo and Sam can reach Mount Doom. Aragorn's army draws out Sauron's remaining forces and empties Mordor, allowing Frodo and Sam to reach the volcano, but Gollum attacks them just as they reach Mount Doom. Sam manages to fend him off, and Frodo enters the volcano. As he stands on the ledge over the volcanic lava, he succumbs to the Ring in front of Sam and claims it as his own, putting it on his finger. Gollum finds the invisible Frodo and attacks him, biting his finger off to reclaim the Ring. Frodo attacks Gollum in an attempt to reclaim the Ring, and in the ensuing struggle they both fall off the ledge. Gollum falls into the lava with the Ring and dies. Frodo clings to the ledge and is rescued by Sam as the Ring disintegrates in the lava. As Frodo and Sam escape, the Eye of Sauron explodes and Mount Doom erupts.
Gandalf flies in with eagles to rescue the Hobbits, who awaken in Minas Tirith and are reunited with the surviving Fellowship. Aragorn is crowned King of Gondor and takes Arwen as his queen. The Hobbits return home to the Shire, where Sam marries Rosie Cotton. A few years later, Frodo departs Middle-earth for the Undying Lands with his uncle Bilbo, Gandalf, and the Elves. He leaves Sam the Red Book of Westmarch, which details their adventures. Sam returns to the Shire, where he embraces Rosie and their children.
Elijah Wood as Frodo Baggins: A young hobbit who continues his quest to destroy the Ring, which continues to torture him.
Sean Astin as Samwise Gamgee: Better known as Sam, Frodo's loyal hobbit gardener and companion.
Andy Serkis as Sméagol Trahald / Gollum: A wretched and treacherous hobbit-like creature who was once one of the river-folk (a race akin to hobbits) and now guides Frodo and Sam into Mordor. The first scene in the film portrays him in his former life as Sméagol, his murder of his relative Déagol for possession of the Ring, as well as his degeneration into Gollum.
Ian McKellen as Gandalf the White: An Istari wizard who travels to aid the Men of Gondor, acting as a general at the Siege of Gondor.
Viggo Mortensen as Aragorn Elessar: A Dúnedain ranger who must finally face his destiny as King of Gondor.
Cate Blanchett as Galadriel: The Elven-Queen of Lothlórien who is aware the time of the elves is at an end.
John Rhys-Davies as Gimli: A dwarf warrior and companion to Aragorn along with Legolas.
Rhys-Davies also voices Treebeard: The ent leader.
Bernard Hill as Théoden: The King of Rohan who, after triumphing at Helm's Deep, is preparing his troops for the Battle of the Pelennor Fields.
Billy Boyd as Peregrin Took: Better known as Pippin, a hobbit who looks into the palantír and later becomes an esquire of Gondor.
Dominic Monaghan as Meriadoc Brandybuck: Better known as Merry, a cousin of Frodo's who becomes an esquire of Rohan.
Orlando Bloom as Legolas Greenleaf: An elven prince of Mirkwood and skilled archer who aids Aragorn in his quest to reclaim the throne.
Hugo Weaving as Elrond: The Elven-King of Rivendell who must convince Aragorn to take up the throne.
Liv Tyler as Arwen Undómiel: Elrond's daughter and Aragorn's true love, who gives up her immortal life for Aragorn.
Miranda Otto as Éowyn: Théoden's niece, who wishes to prove herself in battle and starts to fall in love with Aragorn, who does not return her love. In the extended cut of the film, she finds love with Faramir when they are both residing in the Houses of Healing.
David Wenham as Faramir: A prince of the Stewards of Gondor and head of the Gondorian Rangers defending Osgiliath, who seeks his father's love in vain.
Karl Urban as Éomer: Éowyn's brother, who serves as Chief Marshal of the Riders of Rohan and heir to his uncle's throne.
John Noble as Denethor: The Steward of Gondor and father of Faramir and Boromir, whose grief over Boromir's death and despair over Mordor's superior numbers drive him into madness during the Siege of Gondor.
Ian Holm as Bilbo Baggins: Frodo's elderly uncle, who has rapidly aged after giving away the Ring.
Sean Bean as Boromir: Faramir's brother and a fallen companion of Aragorn, who appears in a flashback of his death at the end of The Lord of the Rings: The Fellowship of the Ring and in the extended cut when his father has a hallucination.
Marton Csokas as Celeborn the Wise: The Elven-King of Lothlórien.
Lawrence Makoare as Witch-King: The lord of the Nazgûl, who leads Mordor's assault on Minas Tirith.
Makoare also plays Gothmog: An Orc commander, who is voiced by Craig Parker.[6]
Thomas Robins as Déagol Nahald: Sméagol's cousin
based on the third volume of J. R. R. Tolkien's The Lord of the Rings. The film is the final instalment in the Lord of the Rings trilogy, preceded by The Fellowship of the Ring (2001) and The Two Towers (2002).