The Great Leviathan (known as the Orichalcos God in the Japanese Version and dubbed the Grand Dragon Leviathan in English advertisement media) was the main antagonist of the story arc Waking the Dragons (though it did not appear true physical form until the final episodes of that arc). It was created by the Orichalcos from the rage of humans, and was believed to be the most powerful creature that ever existed.
Description[]
Dartz, the king of Atlantis, was brainwashed and manipulated by the Orichalcos Stone and told to resurrect their god, the Great Leviathan, by using human souls. It was defeated by the three Legendary Dragons, though Atlantis was sunk in the process. Like Zorc Necrophades, the Great Leviathan was pure evil and wanted nothing more than the extermination of all life on Earth. In order to resurrect the Leviathan, Dartz needed the souls of the three Duelists who wielded the Legendary Dragons cards: Yami Yugi, Seto Kaiba, and Joey Wheeler.
DMx182 Leviathan and Atlantis The Great Leviathan revived.
As more souls were collected, the Leviathan became more and more active, especially as the souls of the Chosen Duelists were collected. After the capture of Joey's soul, a manifestation of the Leviathan began to appear in the sky across the world, and by the time that Kaiba's soul was captured, it was conscious enough to roar from within its astral prison.
Ultimately, Dartz gave up his own soul in order to resurrect the Leviathan after he was unable to acquire Yami Yugi's soul and lost the souls of Kaiba and Joey (Dartz said that his soul was one of "equal" value). Although it overwhelmed the Legendary Knights and an army of monster spirits, Yami managed to draw in the light in the souls that the Leviathan absorbed, and he used that light, released, and called out the three Egyptian Gods. In a battle in the skies over the ocean, Yami Yugi and the Egyptian Gods faced off against the Leviathan. While the Leviathan was seemingly stronger than even the Gods itself, Yami Yugi greatly powered the Egyptian Gods through the light of the captured souls, which proved to be the Leviathan's weakness. Hence, they were able to neutralize the Leviathan, for the light that fueled their power was greater than the darkness that coursed through the Leviathan.
TheGreatLeviathan-JP-Anime-DM-NC The Great Leviathan battling the Egyptian Gods.
Later, Yami Yugi was able to release Dartz from the Leviathan's malignant influence: He did that by using his own light that was represented by the vessel of a memory container to destroy all of the hatred and resentment from the world that powered the Leviathan and vanquished it for good. In the Japanese Version, Dark Magician Girl mentioned that the Leviathan was sent by her to live in the Duel Monsters Spirit World, when the curse of the Orichalcos was extinguished. Atlantis then returned to the bottom of the sea.