J.R.R. Tolkien’s The Lord of the Rings became complete in 1955 when The Return of the King was published.
The first volume, The Fellowship of the Ring, appeared in July 1954. The Two Towers followed later that year, and The Return of the King was published on 20 October 1955.
The final volume covers the War of the Ring’s concluding events, including the fall of Sauron, the restoration of the king, and the return of the hobbits to the Shire. The title refers principally to Aragorn’s return and kingship.
Tolkien’s work was published as three volumes because of practical publishing and production considerations, not because he originally planned a modern trilogy in the usual sense. The complete story is a single long novel divided into six internal books plus appendices.