The Leviathan is a one-time character and a monster of the episode, "Curse of the Deep", from the first season of the animated series, Martin Mystery.
Role in the episode
The Leviathan is revealed to have been the guardian of a sunken ship filled with vast amounts of treasure, and after the ship sank the Leviathan went into hibernation while continuing to guard it.
Centuries later, the Leviathan was disturbed from its slumber by two divers, Stefan and Lance who wished to salvage the treasure on the ship. Attacking the divers, Leviathan succeeded in devouring one, while the other managed to escape with the treasure. In an attempt to reclaim its lost treasure, Leviathan continually attacked a nearby resort in Monte Carlo, Monaco searching out its treasure.
Attempting to track down the Leviathan and to figure out why it was continually attacking the resort, Martin, Diana and Java began an underwater search for the underwater behemoth. Unfortunately, the trio was eaten by the beast. Once inside, the gang and the diver who had been devoured earlier, after fending off Leviathan's immune system managed to formulate a plan to escape Leviathan.
Letting loose all the remaining oxygen in their tanks, Martin and company managed to give Leviathan a "monster version" of the hiccups. The creature shot Martin, Diana, Java and the diver to the surface; there they encountered Stefan who had plundered the ship. Forcing him aside, the gang managed to hurl the Leviathan's treasure back into the ocean. Having reclaimed its treasure the Leviathan stopped its relentless assault on the surface world.
The Leviathan was last seen having been captured by The Center, who planned to transport the creature to an empty part of the ocean, where it could guard its treasure in peace. Within him lived the antibodies: bizarre, small, tentacled creatures found within the stomach of Leviathan, these antibodies are used to attack and destroy any perceived threat. Despite the antibodies being weak singularly, they can be a large threat in groups; they are also, oddly, attracted to bright objects.