Dior Eluchîl is a fictional character in J.R.R. Tolkien's Middle-earth legendarium. He was the son of Beren and Lúthien, and the heir to the throne of Elu Thingol, King of Doriath. Dior was one of the Half-elven. He was also called Eluchîl which means "Heir of Elu", Ausir, "The Wealthy", and Aranel, "The Noble Elf".

Dior lived during the First Age, first in East Beleriand where he was born, and later in Doriath as Thingol's heir-apparent. He married Nimloth and had three children: Eluréd, Elurín and Elwing. After Thingol was slain by the Dwarves who coveted the Nauglamir, Dior became King of Doriath.

Dior and Nimloth were slain by the Sons of Fëanor during the Sack of Menegroth to recapture the Silmaril he inherited from his parents. His sons Eluréd and Elurín were captured during the assault and left to die in the wood of Doriath by Caranthir the Dark, one of the sons of Fëanor. Elwing, however, escaped with the remnant of the Elves of Doriath to the Havens of Sirion, where she wedded Eärendil the Mariner and they together sought pardon and aid from the Valar.

See also:
Oath of Fëanor
War of Wrath

In the Third Age, Dior is also the name of one of the Ninth Ruling Steward of Gondor.