Which of J.R.R. Tolkien’s children completed and edited The Silmarillion?

Christopher Tolkien completed and edited The Silmarillion after J.R.R. Tolkien’s death.

J.R.R. Tolkien worked on the mythology behind The Silmarillion for decades, but he died in 1973 before producing a final publishable form. Christopher Tolkien organized the manuscripts, selected and edited material, and prepared the work for publication with assistance from Guy Gavriel Kay.

The Silmarillion was published in 1977. It presents the creation of Tolkien’s world, the history of the Valar, the Elves, the First Age, Númenor, and events leading toward the later history of Middle-earth. Because the surviving papers contained differing versions and unfinished passages, editorial decisions were unavoidable.

Christopher later edited and published many additional volumes from his father’s papers, including Unfinished Tales and the twelve-volume History of Middle-earth. He was therefore not the author of the underlying mythology, but he was crucial to making a coherent published edition available.