The Reaper Leviathan is a large aquatic creature from the video game Subnautica. At 55 metres long it is considered the fifth largest creature in the game. It lives three areas on Planet 4546B, namely the crash zone of the Aurora, the Dunes biome and the Mountains biome. Using its large mandibles it is able to cause large amounts of damage to a submarine. The roars emitted by Reapers are a form of sonar they use for location of prey.
The "Leviathan" part of their name is not actually part of their name, rather a classification given to very large creatures.