Leviathans are a race of giant creatures found in the The Legend of Zelda series. They often resemble sea-creatures, although they do not always reside in the sea. The Leviathan term and race appear in-game only in The Legend of Zelda: Breath of the Wild, and are only indirectly referred to in some previous episodes.
Leviathans are ancient giant whales and fish thought to have gone extinct many thousands of years before. There are bones located high up in the Hebra Mountains, Eldin Mountains, and the Gerudo Desert. Each appear to be three different species based on the skulls.
There are researchers that each have a theory as to why they died out. One believes they died out during a great ice age, another believes they died out due to a severe prolonged drought, and third believes they were destroyed by a cataclysmic volcanic eruption.
The Wind Fish is the first of the great flying leviathan whales to debut in the series.
The Legend of Zelda: Ocarina of Time and Oracle games
Lord Jabu-Jabu, the patron deity of the Zoras, is a mammoth fish who has lived in a secluded fountain behind King Zora's throne for centuries. The leviathan is covered in ornate markings, which symbolizes his exalted position in Zoran culture.
Lord Jabun is a giant fish who is thought to be descended from Lord Jabu-Jabu.
Levias is a giant flying whale - similar to the Wind Fish - and also takes his name from the word "Leviathan".
Levias appears in the Skyloft level of the game. Several times throughout the level, Fi delivers Pumpkin Soup to Levias, escorted by Link. When given a bottle of soup, Levias pushes a rock to create a path for the heroes. Later when Link and Fi are having trouble fighting Volga, Levias states that if he was at full power he could help them defeat Volga. Link seeks out the Great Fairy living in the Fairy Fountain on Skyloft. After she is summoned by the Magic Circle located in her fountain, Levias is fed a giant pumpkin dangling from a fishing pole by the Great Fairy's fairy servants, which empowers Levias enough to weaken Volga, allowing Fi and Link to defeat him.
Levias also appears as part of Link's Great Fairy moveset, where he is summoned by the Great Fairy during one of her combos to unleash a deluge of lightning on enemies.