An early version of Peter Jackson's The Lord of the Rings: The Return of the King turned heroic hobbit Frodo (Elijah Wood) into a murderer. In the early 2000s, the Lord of the Rings films redefined the fantasy genre and became the gold-standard for cinematic epics. The trilogy began in 2001 with The Fellowship of the Ring and concluded in 2003 with Return of the King. Amazingly, Return of the King won 11 Academy Awards, which was every single award it was nominated for. This included Best Picture, and to this day, it is one of the few fantasy films to be recognized as such by the Academy. The film starred Wood, Viggo Mortensen, Orlando Bloom, Sean Astin, John Rhys-Davies, and Ian McKellen.
Return of the King brought Frodo's journey to a close, and while the last scenes of the film are both peaceful and bittersweet, Frodo goes through a great deal before achieving that peace. Throughout the trilogy, Frodo grapples with the temptation posed by the Ring. At the climax of the film, Frodo reaches Mount Doom, the only place the Ring can be destroyed, with his loyal friend Samwise Gamgee (Astin). Frodo is attacked by Gollum (Andy Serkis), the former hobbit who has been driven mad by the Ring's power. In the film, the two struggle over the Ring before toppling over the ledge above the volcano; while Frodo recovers, Gollum does not, and both he and the Ring are consumed by the fires of Mount Doom. However, that wasn't Jackson's original plan.
In Jackson's 2006 biography, Peter Jackson: A Film-maker's Journey (via WinterIsComing.net), it says Jackson and his team initially planned to have Frodo push Gollum off the ledge himself, which Jackson described as "straight-out murder." Despite having shot that version, Jackson had his doubts about Frodo's murderous turn, and that was largely because of J.R.R. Tolkien, the author of the Lord of the Rings books. Jackson believed this change "flew in the face of everything that [Tolkien] wanted his heroes to be."
In the book, Gollum falls off the ledge after biting Frodo's finger off, regaining the Ring, and celebrating his victory. However, Jackson also had issues accepting that version because it took Frodo out of the moment entirely. This was why he ultimately came up with the idea to have Frodo and Gollum struggle for the Ring before Gollum took his fatal fall.
The final version of Frodo and Gollum's climatic moment in Return of the King was probably the best option for Jackson to have taken. While Frodo killing Gollum would have added a new layer to his character, Jackson made a good point in thinking it went against Tolkien's writing. That decision could have alienated fans, as evidenced by the reactions to some of Jackson's choices with the Hobbit films. The Lord of the Rings trilogy was especially praised for how well it adapted Tolkien's novels, and it's clear Jackson took the responsibility seriously.
Source: Peter Jackson: A Film-maker's Journey (via WinterIsComing.net)