Eowyn shieldmaiden of Rohan © 2009
In The Lord of the Rings Éowyn, a daughter of the House of Eorl and the niece of King Théoden, is introduced in Meduseld, the king's hall at Edoras. She was the daughter of Théodwyn (sister to Théoden) and Éomund, and the sister of Éomer. When she was only three years old, her father was killed fighting Orcs and her mother died of grief. Éowyn and Éomer were raised in her uncle's household as if they were his own children.
Tolkien writes she fell into depression since she longed to win renown in battle - more so because she was noble - but being female, her duties were reckoned to be at Edoras. When Théoden's mind was poisoned by his adviser Gríma Wormtongue, Éowyn was obliged to care for her uncle, and his deterioration pained her deeply. To make matters worse, she was stalked by Gríma.
However, when Gandalf (along with Aragorn, Legolas, and Gimli) arrived, he healed Théoden from Wormtongue's corruption, and Éowyn became infatuated with Aragorn. It soon became clear that Aragorn could not return her love (though he did not mention his betrothal to Arwen), and would not allow her to join him in going to war. As Aragorn pointed out, her duty was with her people; she had to shoulder the responsibility of ruling Rohan in Théoden's stead when the war-host of Rohan went to war. Aragorn also said her duties were no less valiant. Likening her situation to a "cage", Éowyn said she feared
"...[t]o stay behind bars, until use and old age accept them, and all chance of great deeds is gone beyond recall or desire."
Frustrated by unrequited love for Aragorn and longing for death in battle, she disguised herself as a man and under the alias of Dernhelm, travelled with the Riders of Rohan to the Battle of the Pelennor Fields outside the White City of Minas Tirith in Gondor, carrying with her Merry, who had also been ordered to remain behind.
During the battle of the Pelennor Fields, she confronted the Witch-king of Angmar, Lord of the Nazgûl, after Théoden was injured. The Witch-king threatened to "bear [her] away to the houses of lamentation, beyond all darkness, where [her] flesh shall be devoured, and [her] shriveled mind be left naked to the Lidless Eye." The Witch-king further boasted that "[n]o living man may hinder me," referring to the 1,000-year-old prophecy by the Elf-lord Glorfindel, foretelling that the Witch-king would not fall "by the hand of man". Éowyn then removed her helmet and declared:
"But no living man am I! You look upon a woman. Éowyn I am, Éomunds daughter. You stand between me and my lord and kin. Begone, if you be not deathless! For living or dark undead, I will smite you, if you touch him."
The Witch-king attacked Éowyn with his steed, but she slew it. He then broke her shield-arm with his mace, but was distracted by Merry, who stabbed him behind the knee with a sword enchanted with spells against him. Éowyn seized the opportunity to strike a killing blow, stabbing him "between crown and mantle".
Severely injured, Éowyn was believed dead until Prince Imrahil of Dol Amroth realized she still lived. Because of the poisonous effect of the Black Breath of the Nazgûl and her hopeless love for Aragorn, she faced near-certain death and was brought up to the Houses of Healing together with Merry. However, she was treated in time by Aragorn. Éomer, while not blaming Aragorn, believed that unrequited love was at the root of her depression. Aragorn answered that she loved Éomer more truly than himself, as her feeling for Aragorn was largely fantasy about the idea of Aragorn as a great leader and warrior representing the heroic life she could not have; and Gandalf pointed out the deeper roots of her depression.
While recuperating in the Houses of Healing, she met Faramir, with whom she soon fell in love, understanding that her previous "love" for Aragorn was mainly hero-worship. Her outlook on life also changes:
"Then the heart of Éowyn changed, or else she understood it... ...'I will be a shieldmaiden no longer, nor vie with the great Riders, nor take joy only in the songs of slaying. I will be a healer, and love all things that grow and are not barren.'"
After the demise of Sauron, the happily wedded couple settled in Ithilien, of which Faramir was made the ruling Prince by King Elessar (the name with which Aragorn ascended the throne of the Reunited Kingdom). Faramir and Éowyn had at least one son (likely Elboron), and their grandson was Barahir, who wrote The Tale of Aragorn and Arwen in the Fourth Age. Tolkien nowhere gives the cause and date of Éowyn's death, but one can presume she died of natural causes, in peacetime.