Who are Beren and Lúthien in J R R Tolkien's story that will be published a century after it was written?

Answer 1

First: spoiler alert. Though really they shouldn't be very big spoilers; a version of Beren and Luthien's story was published in the Silmarillion in the 1970s.

Short version:

Beren and Luthien are the ancestors of the Half-Elven. They're Elrond's great-grandparents on his mother's side, and therefore Arwen's great-great grandparents. They're the great-to-the-several-dozenth grandparents of Aragorn.

Longer version (though it's still shorter than the Tale of Beren and Luthien):

Luthien was the daughter of King Thingol ("Greycloak"), the Elven king of Doriath in Beleriand, and his wife Melian the Maia (the Maiar aren't mentioned much in by name in The Lord of the Rings, but Gandalf, Saruman, Radagast, and presumably the two otherwise unmentioned "blue wizards" are also Maiar). Beren was the great-great grandson of Bëor, leader of the first tribe of Men to meet and befriend Elves.

Thingol also known as Elwë, disliked Men and did not wish his daughter to marry Beren, so he set an extremely high bride-price for her: nothing less than a silmaril from the iron crown of Morgoth, Sauron's master. Beren and Luthien eventually did get married, but since Beren was a mortal Man fated to die and Luthien was an immortal Elf (Elves can be killed, but they do not die of old age), Luthien ... and later her descendants ... were given the choice to remain immortal, and live on after Beren died, or to accept the Gift of Men (death) and become mortal, dying with him.

Their only son Dior was killed in his thirties, so the choice wasn't much of an issue for him. Dior's son Elros (from whom Aragorn is descended) chose mortality, and his other son Elrond chose immortality. THEIR decendants seem for the most part to have been locked into the choice made by these brothers, though Elrond's daughter Arwen, upon marrying Aragorn, was given the same options as her great-great grandmother and made the same choice.