The Tolkien work published posthumously in 1977 as a collection of myths about the First Age was The Silmarillion.
The book was edited and arranged by Christopher Tolkien from writings developed by J.R.R. Tolkien over many decades. It presents the creation of the world, the history of the Valar, the awakening of the Elves, and the wars against Morgoth.
Its central jewels are the Silmarils, three radiant gems made by Fëanor. Their theft by Morgoth drives much of the tragic history of the First Age and leads to long conflicts among Elves, Men, and other peoples.
The Silmarillion is not a conventional novel with one continuous narrative. It includes mythic accounts, annals, genealogies, and legends in different styles. Unfinished Tales, published later, contains additional narratives and background material.