Time travel in The Lord of the Rings in the context of "Legendarium"

Tolkien's legendarium is the body of J. R. R. Tolkien's mythopoeic writing, unpublished in his lifetime, that forms the background to his The Lord of the Rings, and which his son Christopher summarized in his compilation of The Silmarillion and documented in his 12-volume series The History of Middle-earth. The legendarium's origins reach back to 1914, when Tolkien began writing poems and story sketches, drawing maps, and inventing languages and names as a private project to create a mythology for England. The earliest story, "The Voyage of Earendel, the Evening Star", is from 1914; he revised and rewrote the legendarium stories for most of his adult life.

The Hobbit (1937), Tolkien's first published novel, was not originally part of the larger mythology but became linked to it. Both The Hobbit and The Lord of the Rings (1954 and 1955) are set in the Third Age of Middle-earth, while virtually all of his earlier writing had been set in the first two ages of the world. The Lord of the Rings occasionally alludes to figures and events from the legendarium to create an impression of depth, but such ancient tales are depicted as being remembered by few until the story makes them relevant.

Isildur (Quenya: [iˈsildur]) is a fictional character in J. R. R. Tolkien's Middle-earth, the elder son of Elendil, descended from Elros, the founder of the island Kingdom of Númenor. He fled with his father when the island was drowned, becoming in his turn King of Arnor and Gondor. He cut the Ring from Sauron's hand, but instead of destroying it, was influenced by its power and claimed it for his own. He was killed by orcs, and the Ring betrayed him by slipping off his finger just before his death. The Ring then became lost in the River Anduin. This set the stage for the Ring to pass to Gollum and then to Bilbo, as told in The Hobbit; that in turn provided the central theme, the quest to destroy the Ring, for The Lord of the Rings.

Tolkien began a time-travel story, The Lost Road, in which a father and a son were to reappear time and again in human families throughout history. One of the appearances was to be in Númenor just before its fall, with the father as Elendil and the son as Herendil, later called Isildur. The story was abandoned, but Tolkien reused the characters and events.