Which J.R.R. Tolkien story was published posthumously in 1977 as a collection of mythic tales?

The Silmarillion was published posthumously in 1977 as a collection of J.R.R. Tolkien’s mythic tales.

Tolkien died in 1973, leaving behind many versions of the stories that became The Silmarillion. His son Christopher Tolkien organized, edited, and shaped the material for publication, with assistance from Guy Gavriel Kay. The book appeared on 15 September 1977, four years after Tolkien’s death.

Unlike The Hobbit and The Lord of the Rings, The Silmarillion is not a single continuous adventure centered on one protagonist. It presents the creation of Tolkien’s world, the history of the Valar and Elves, the First Age wars, and later events. Its opening section is “Ainulindalë,” followed by “Valaquenta” and “Quenta Silmarillion.” Readers sometimes confuse it with Unfinished Tales, another posthumous collection published in 1980.