Elrond Half-elven is a fictional character in J. R. R. Tolkien's Middle-earth legendarium. Both of his parents, Eärendil and Elwing, were half-elven, having both Men and Elves as ancestors. He is the bearer of the elven-ring Vilya, the Ring of Air, and master of Rivendell, where he has lived for thousands of years through the Second and Third Ages of Middle-earth. He was the Elf-king Gil-galad's herald at the end of the Second Age, saw Gil-galad and king Elendil fight the dark lord Sauron for the One Ring, and saw Elendil's son Isildur take it rather than destroy it.

He is introduced in The Hobbit, where he plays a supporting role, as he does in The Lord of the Rings and The Silmarillion. Scholars have commented on Elrond's archaic style of speech, noting that this uses genuinely archaic grammar, not just a sprinkling of old words. The effect is to make his speech distinctive, befitting his age and status, while remaining clear, and avoiding quaintness. He has been called a guide or wisdom figure, a wise person able to provide useful counsel to the protagonists. It has been noted that just as Elrond prevented his daughter Arwen from marrying until conditions were met, so Tolkien's guardian, Father Francis Xavier Morgan, prevented Tolkien from becoming engaged or marrying until he came of age.

Elrond was born in the First Age at the refuge of the Mouths of Sirion in Beleriand, the son of the half-elven mariner Eärendil and Elwing his wife, and a great-grandson of Beren and Lúthien. Not long afterwards, the havens were destroyed by the sons of Fëanor, who captured Elrond and his brother Elros. Their parents feared that they would be killed; instead, they were befriended by Fëanor's sons Maedhros and Maglor. Like his parents but unlike his brother, Elrond chose to be counted among the Elves when the choice of kindreds was given to him. When Beleriand was destroyed at the end of the First Age, Elrond went to Lindon with the household of Gil-galad, the last High King of the Noldor.

During the War of the Elves and the dark lord Sauron in the Second Age, the king Gil-galad sent Elrond to the defence of Eregion against the Dark Lord. Sauron destroyed Eregion and surrounded Elrond's army, but the dwarf-king Durin and the elf-king of Lórien, Amroth, attacked Sauron's rearguard. Sauron turned to fight them, and drove them back to Moria. Elrond was able to retreat north to a secluded valley, where he established the refuge of Imladris, later called Rivendell; he lived there through the Second and Third Ages.

Near the end of the Second Age, the Last Alliance of Elves and Men was formed, and the army departed from Imladris to Mordor, led by Elendil and Gil-galad. Sauron killed both of them at the end of the siege of Barad-dûr. Elrond saw Elendil's son Isildur destroy Sauron's physical body and take the One Ring for himself; Elrond and Cirdan urged Isildur to destroy it, but he refused. Elrond served as Gil-galad's herald, and he and Círdan were entrusted with the two Elven Rings that Gil-galad held. Elrond and Círdan were the only ones to stand with Gil-galad when he fell.

Elrond married Celebrían, daughter of Celeborn and Galadriel, early in the Third Age. The place and date of Celebrían's birth are not specified. In the version of their history that describes Galadriel and Celeborn as rulers of Eregion in the Second Age, Galadriel and Celebrían left Eregion for Lórinand as Sauron's influence over Eregion grew. According to one account, Celebrían and her parents later lived for many years in Rivendell (Imladris). Celebrían and Elrond had three children: the twins Elladan and Elrohir, and Arwen Undómiel (Evenstar).

On a trip from Rivendell to Lórien, Celebrían was waylaid by Orcs in the Redhorn Pass on Caradhras in the Misty Mountains. She was captured and tormented and received a poisoned wound. She was rescued by her sons and healed by Elrond, but "after fear and torment" she could no longer find joy in Middle-earth, so she passed to the Grey Havens and over the Sea to Valinor in the following year.

Elrond was an ally of the North-Kingdom of Arnor. Following its fall, Elrond harboured the Chieftains of the Dúnedain (the descendants of the Kings of Arnor) and the Sceptre of Annúminas, Arnor's symbol of royal authority. When Aragorn's father Arathorn was killed a few years after Aragorn's birth, Elrond raised Aragorn in his own household and became a surrogate father to him. Aware of his daughter Arwen's feelings for Aragorn, Elrond would permit their marriage only if Aragorn could unite Arnor and Gondor as High King.