The Reaper Leviathan is a hostile predator from Subnautica, the underwater survival game developed by Unknown Worlds Entertainment and fully released in 2018. Its roar is the sound players hear just before one of the game's most feared creatures attacks in the Crash Zone and other open waters. Clips of the scream spread through gameplay videos, reaction compilations and horror edits, where it became shorthand for sudden underwater danger. It remains popular because that single roar instantly tells even non-players that something enormous and hostile is nearby.