What was J.R.R. Tolkien’s first published Middle-earth legendarium work?

J.R.R. Tolkien’s first published Middle-earth legendarium work was The Hobbit.

Published in 1937, The Hobbit introduced a version of the world that Tolkien would later call Middle-earth. Its plot follows Bilbo Baggins on a journey with Gandalf and Thorin Oakenshield’s company to reclaim Erebor from Smaug. The book’s tone is lighter and more directly shaped by children’s literature than that of Tolkien’s later works.

Tolkien had been developing related myths, languages, and histories for years before The Hobbit appeared. Much of this material was unpublished during his lifetime and was later edited by his son Christopher Tolkien. The Lord of the Rings followed as a more ambitious sequel, appearing between 1954 and 1955.

The Silmarillion is often named by mistake because it contains the deepest account of Tolkien’s mythology. However, it was published posthumously in 1977, nearly four decades after The Hobbit, and was assembled from Tolkien’s extensive unfinished writings.