The Gargantuan Leviathan comes from Return of the Ancients, a fan-made mod that expands the underwater world of Subnautica with new leviathan-class creatures. Its roar was collected from gameplay footage showcasing every sound made by the creature, and the clip later circulated on soundboards for fans who wanted the effect without playing the mod. It remains popular because Subnautica players recognise the creature instantly, and creators outside the game use the deep, threatening bellow as a shorthand for something enormous lurking beneath the water.