The sound comes from Peter Jackson's The Lord of the Rings films, where the horns of Rohan announce the Riders of Rohan, the horse-lords led by King Théoden. Its most famous use is the dawn charge at the Battle of the Pelennor Fields in The Return of the King from 2003, a scene widely shared and parodied online. Fans clipped the horn call on its own because it instantly signals reinforcements arriving, and editors now reuse it far beyond fantasy edits for any last-minute heroic arrival.