Arwen Undómiel is a character in J. R. R. Tolkien's legendarium. She appears in his best-known novel, The Lord of the Rings, usually published in three volumes. Arwen is one of the Half-elven who lived during the Third Age.
As told in "The Tale of Aragorn and Arwen", found in Appendix A to The Lord of the Rings (after the third volume, The Return of the King), during Aragorn's twentieth year he met Arwen for the first time in Rivendell, where he lived under Elrond's protection. Arwen, then over 2700 years old, had recently returned to her father's home after living for a while with her grandmother Galadriel in Lórien. Aragorn fell in love with Arwen at first sight. About thirty years later, the two were reunited in Lórien; at that time, Arwen reciprocated Aragorn's love; then they "plighted their troth" (promised themselves to each other) on the mound of Cerin Amroth.
Arwen's first appearance in The Lord of the Rings proper was at Rivendell, when the Hobbits arrived there, and Aragorn was seen with her — the first hint of their relationship. Later, when the Fellowship of the Ring came to Lothlórien, Aragorn remembered their earlier meeting and paused in reverence on Cerin Amroth.
Arwen entered the story again when, before taking the Paths of the Dead, Aragorn was met by a group consisting of Dúnedain (his people, from the North), and Arwen's brothers, Elladan and Elrohir. They brought to him a banner of black cloth: a gift made by Arwen, and a sign that encouraged him to take the difficult path. When the banner was unfurled at the Battle of the Pelennor Fields to reveal the emblem of Elendil in mithril, gems, and gold, it was the first triumphant announcement of the King's return.
The four passages described above are Arwen's only appearances in the story as it stands, not counting The Tale of Aragorn and Arwen. Judging only by visibility, Arwen is mostly a minor character in Tolkien's The Lord of the Rings proper, but she nevertheless appears in detail in its Appendices. Also, she plays a role in the plot which is disproportionate to the number of scenes in which she appears. Arwen served as inspiration and motivation for Aragorn, who, as Elrond had stipulated, had to become no less than King of Gondor and Arnor before he could wed her. When Éowyn fell in love with Aragorn it was his fidelity to Arwen that prevented him from reciprocating. This partly motivated Éowyn's subsequent death-wish heroism during the Battle of the Pelennor Fields, which had major repercussions for the defence of Middle-earth.
The Tale of Aragorn and Arwen relates that Arwen had a son, Eldarion, and at least two unnamed daughters by Aragorn. She gave up her life and died of a broken heart in 121 of the Fourth Age, at Cerin Amroth, one year after the death of Aragorn. At the time, she was 2,901 years old.
Arwen was a very distant relative of her husband Aragorn. Aragorn's ancestor, Elros Tar-Minyatur, the first King of Númenor, was her father Elrond's brother, who chose to live as a Man rather than one of the Eldar. Arwen eventually became Queen of the Reunited Kingdom of Arnor and Gondor when she married Aragorn, who was of the line of the Kings of Arnor. By Arwen and Aragorn's marriage, the long-sundered lines of the Half-elven were joined. Their union also served to unite and preserve the bloodlines of the Three Kings of the High Elves (Ingwë, Finwë, and the brothers Olwë and Elwë) as well as the only line with Maiarin blood through Arwen's great-great-great grandmother, Melian, Queen of Doriath, and also on Aragorn's side, through the line of kings of Arnor and Númenor to Elros, Elrond's brother, whose great-great-grandmother was also Melian.
In Peter Jackson's The Lord of the Rings film trilogy, Arwen is played by Liv Tyler. Many additional scenes pertaining to Arwen are inserted, practically all of which deviate from the novel and some of which seem inspired by the Tale.
In the first film, Arwen sneaks up to find Aragorn and single-handedly rescues Frodo Baggins from the Black Riders at Bruinen, thwarting them with a sudden flood, summoned by an incantation. In the book, Glorfindel put Frodo on horseback and sent him alone to flee the Black Riders, and Elrond and Gandalf arranged the flood. In the book, Frodo makes his own stand against the Black Riders; in the movie Arwen defends him. During this flight, Arwen wields the sword Hadhafang, stated in film merchandise to have once been wielded by her father. This sword is actually the sword of Idril Celebrindal, Arwen's great-grandmother. It is original, though the name is derived from Tolkien's writings.
Following the aforementioned scenes, the deviations include a scene in which Aragorn is injured and has a dream about Arwen (who kisses him), a scene where Arwen has an argument with her father about leaving for Valinor, and a scene where she (with Figwit) departs for Valinor and then suddenly returns when she has a vision of her future son, Eldarion. (Surprising to her, not because a union with Aragorn could produce a child, but rather that her father had only prophesied death in her future.)
Throughout the War of the Ring, Elrond begs her to accompany her kin to the Undying Lands because he does not wish to see another of his family die, but after she initially embarks for the Grey Havens to sail away, she returns to Rivendell and thereafter refuses to leave Middle-earth because of the love she bore for Aragorn.
In the film version of The Return of the King Arwen rides back from the road to the Grey Havens. Elrond takes the reforged Narsil, now Andúril, to Aragorn at Dunharrow, and tells him that her fate has become bound with the One Ring, and that she is dying. How this came to be is left unexplained. In the books, Narsil was reforged before the Fellowship left Rivendell, and Arwen's life is never linked to the struggle to destroy the Ring. The movies also portray that through her love to Aragorn, she became human, an important factor also within the book, in which Arwen echoes the choice and fate of her ancestor Lúthien to become a mortal woman.
The trilogy invents a jewelled pendant called the Evenstar which Arwen gives to Aragorn as a reminder of their love. The Evenstar pendant also appears in Electronic Arts' The Battle for Middle-earth series of real-time strategy games. It gives powers, purchased by power points, to the forces of good, as opposed to the One Ring which gives powers to the forces of evil. In the novel, Arwen gives a similar necklace to Frodo before he leaves Minas Tirith.
In earlier copies of the script (when the movies were supposed to be filmed in two parts under another production company), Arwen fought in the Battle of Helm's Deep and brought the sword Andúril to Aragorn. However, both Liv Tyler and the writers felt that the character's involvement in Helm's Deep was inappropriate, and left her out of the sequence.