The Silmarillion was published posthumously in 1977 and describes the history of Middle-earth before The Hobbit.
Tolkien worked on the legends behind The Silmarillion for much of his life. The book covers the creation of the world, the divine beings called the Valar, the first age of the Sun, the history of the Silmarils, and the downfall of Númenor. It also contains material about figures such as Fëanor, Beren, Lúthien, Túrin, and Eärendil.
Tolkien died in 1973, leaving the work in different versions and states of completion. His son Christopher Tolkien edited the materials into the published volume, which appeared four years later. It is therefore not a novel revised and completed by J.R.R. Tolkien alone.
Unfinished Tales, published in 1980, is another posthumous collection, but it is not the book that presents Tolkien’s broad mythological history in this form.