The Lord of the Rings: The Return of the King is a 2003 epic high fantasy adventure film directed by Peter Jackson from a screenplay he wrote with Fran Walsh and Philippa Boyens. It is based on 1955's The Return of the King, the third volume of the novel The Lord of the Rings by J. R. R. Tolkien. The sequel to 2002's The Lord of the Rings: The Two Towers, the film is the third and final instalment in The Lord of the Rings trilogy. It has an ensemble cast including Elijah Wood, Ian McKellen, Liv Tyler, Viggo Mortensen, Sean Astin, Cate Blanchett, John Rhys-Davies, Bernard Hill, Billy Boyd, Dominic Monaghan, Orlando Bloom, Hugo Weaving, Miranda Otto, David Wenham, Karl Urban, John Noble, Andy Serkis, Ian Holm, and Sean Bean. Continuing the plot of the previous film, Frodo and Sam follow Gollum toward Mount Doom to destroy the One Ring, unaware of Gollum's intentions to betray the duo to take the ring for himself, while Merry, Pippin, Gandalf, Aragorn, Legolas, Gimli and their allies join forces against Sauron and his legions from Mordor.

The Return of the King was financed and distributed by American studio New Line Cinema, but filmed and edited entirely in Jackson's native New Zealand, concurrently with the other two parts of the trilogy. It premiered on 1 December 2003 at the Embassy Theatre in Wellington and was then released on 17 December 2003 in the US and 18 December 2003 in New Zealand. The film was acclaimed by critics and audiences, who considered it a landmark in filmmaking and the fantasy film genre, and a satisfying conclusion to the trilogy, with praise for the visual effects, performances, action sequences, direction, screenplay, musical score, costume design, emotional depth, scope, and story. It grossed over $1.1 billion worldwide, becoming the highest-grossing film of 2003, the second-highest-grossing film of all time during its run, Jackson's highest-grossing film, and the highest-grossing film ever released by New Line Cinema.

Like the previous films in the trilogy, The Return of the King is widely recognised as one of the greatest and most influential fantasy films ever made. The film received numerous accolades; at the 76th Academy Awards, it won all eleven awards for which it was nominated, including Best Picture, the first fantasy film to do so and tying with 1959's Ben-Hur and 1997's Titanic as the movie with the most Academy Award wins. It also became the second film series whose entries have all won Best Visual Effects, after the original Star Wars trilogy.