In Norse mythology, Gjallarhorn is the great horn of Heimdall, the watchman of the gods, said to be blown to announce Ragnarök, the end and rebirth of the world. That association with a world-changing alarm has made the name shorthand for an epic horn call in games, fantasy stories and online videos. Clips like this one circulate as a standalone sound effect rather than a line from a single film or show, and creators reuse it whenever a moment needs to feel ancient, momentous and larger than life.