Elu Thingol or Elwë Singollo is a fictional character in J.R.R. Tolkien's Middle-earth legendarium. He appears in The Silmarillion, The Lays of Beleriand and The Children of Húrin and in numerous stories in The History of Middle-earth. The King of Doriath, King of the Sindar Elves, High-king and Lord of Beleriand, he is a major character in the First Age of Middle-earth and an essential part of the ancestral backgrounding of the romance between Aragorn and Arwen in The Lord of the Rings. Alone among the Elves, he married an angelic Maia, Melian.

The Silmarillion is a book consisting of a collection of myths and stories in varying styles by the English writer J. R. R. Tolkien. It was edited and published posthumously by his son Christopher Tolkien in 1977, assisted by Guy Gavriel Kay, who became a fantasy author. It tells of Eä, a fictional universe that includes the Blessed Realm of Valinor, the ill-fated region of Beleriand, the island of Númenor, and the continent of Middle-earth, where Tolkien's most popular works—The Hobbit and The Lord of the Rings—are set. After the success of The Hobbit, Tolkien's publisher, Stanley Unwin, requested a sequel, and Tolkien offered a draft of the writings that would later become The Silmarillion. Unwin rejected this proposal, calling the draft obscure and "too Celtic", so Tolkien began working on a new story that eventually became The Lord of the Rings.