Which son of J.R.R. Tolkien edited and assembled The Silmarillion for publication?

Christopher Tolkien edited and assembled The Silmarillion for publication.

J.R.R. Tolkien died in 1973, leaving a large body of stories, drafts, notes, and linguistic material about the history of Middle-earth. Christopher Tolkien worked through these papers, selected related texts, and shaped them into a publishable volume. The Silmarillion appeared in 1977, four years after his father's death.

The book presents mythic and historical material from the creation of Eä through the First Age, including the stories of the Valar, the Elves, the Silmarils, and the wars against Morgoth. It is not a finished manuscript arranged by its author in the same way as The Hobbit. Christopher's editorial decisions were therefore essential to the book's final form. He later edited many additional collections, including Unfinished Tales and the twelve-volume History of Middle-earth.