Bellum

Evil Phantom, Bellum is the primary antagonist of The Legend of Zelda: Phantom Hourglass. He is a squid-like creature with a single eye in his mouth, along with many more eyes on his tentacles. Until the conclusion of the fourth dungeon, Link and Linebeck are unaware of his existence. However, once a petrified Tetra is found, Oshus, revealed to be the Ocean King Umiou himself, appears to tell the two about what happened to her. Many years ago, Bellum appeared and began to consume the Force, an energy which everything in the world possesses. Bellum attacked Umiou, who naturally fought back. However, his attacks were useless, as Bellum could absorb the Force. Umiou was locked away, and Bellum began consuming all of his Force. Bellum then used the Sands of Time, a crystallized version of the Force, to create monsters to seal away the Fairies of Power, Wisdom, and Courage. He also created the Ghost Ship, spreading rumors of a great treasure within it to lure people there. The Phantoms, found within the Temple of the Ocean, are his alter-egos, powerful and nigh-invincible like himself. He was attracted to Tetra because of the great amount of Force within her.

Umiou reveals that the only way to slay Bellum is with the legendary Phantom Sword, a sword which only the blacksmith Zauz knows how to forge. After many struggles, Link obtains the Scarlet Steel, the Azure Steel, and the Verdure Steel needed to forge the Phantom Sword. He then finally penetrates the inner sanctums of the Temple of the Ocean, where Bellum dwells, and uses the power of both the Phantom Sword and the Phantom Hourglass to temporarily defeat it. However, Bellum soon takes a revived Tetra and takes control of the Phantom Ship, attempting to escape with her. With the combined efforts of both Link and Linebeck, however, the Ghost Ship is destroyed. Bellum, still relentless, makes a large piece of the Ghost Ship drop onto the boat. Umiou, who was still on it, is seemingly killed, and Bellum uses this as an opportunity to grab Link. Linebeck, however, manages to free him using the Phantom Blade, but is soon taken by Bellum instead.

In a last-ditch effort to defeat Link, Bellum takes control of Linebeck, transforming him into an immense knight. He then attacks Link, whose attacks against it are initially useless, even with the Phantom Hourglass. Ciela, however, goes behind the Bellum-possessed Linebeck, allowing Link to know when Bellum's weak point, his eye, is open. Bellum uses one of his tentacles to trap Ciela, though, and continues fighting Link. Link manages to loosen Bellum's grip on Ciela several times throughout the battle, giving him Phantom Spheres to freeze time once Bellum's eye is open. After a long and difficult battle, Linebeck is freed from Bellum's clutches, and the beast turns to the last of the Sands of Time. Link absorbs it with the Phantom Sword, and Bellum is defeated.

Miscellaneous
Bellum is the latin word for war.

Trivia

 * The relationship between Bellum and the Ocean King is ironic. Bellum's design is obviously a squid whereas the Ocean King is a whale. Most whales and squids are natural enemies and this is the case in this story.