Which Tolkien story was first published in 1977 by Christopher Tolkien?

The Silmarillion was first published in 1977 by Christopher Tolkien.

J.R.R. Tolkien’s The Silmarillion appeared posthumously on 15 September 1977. Christopher Tolkien edited and arranged material left by his father, with assistance from the writer Guy Gavriel Kay. The book presents a mythic history of Arda, beginning with its creation and continuing through the First Age and later events.

Unlike The Hobbit and The Lord of the Rings, The Silmarillion is not a single continuous adventure novel. It contains several interconnected sections, including the Ainulindalë, Valaquenta, Quenta Silmarillion, Akallabêth, and Of the Rings of Power and the Third Age.

Readers sometimes confuse it with Unfinished Tales, another posthumous collection edited by Christopher Tolkien and published in 1980. The Children of Húrin was published much later, in 2007, as a more complete presentation of one tragic First Age story.