Bellum

Bellum is the primary antagonist of The Legend of Zelda: Phantom Hourglass and its only appearance so far, though his Phantom minions (who are made from Bellum) appear in Spirit Tracks, so he survived through them. He resembles a squid, with an eye on the end of each of his five purple tentacles. He has a sixth eye on the center of his body, which is his weak point.

He has two titles, the Evil Phantom and the Phantom Devil.

Biography
This biography of Bellum is organized into the latest "official Zelda timeline", this may change completely in the future as the timeline given is merely meant as an example, and their have been official timelines before it.

Adult Timeline
This is the timeline where Ganondorf was sealed after ruling Hyrule and then being defeated by Link, he eventually escaped, leading to the backstory of The Wind Waker.

The Legend of Zelda: Phantom Hourglass
His origins are unknown but he appeared in the World of the Ocean King and drained the Ocean King's life force. To survive, he split his power into two, with Bellum absorbing the majority of his power and turning it into Sand of Hours, which he used to create six evil monsters named Blaaz, Cyclok, Crayk, Dongorongo, Gleeok, and Eox. The Ocean King lived on in the form of an old man named Oshus.

At some point, Bellum placed a curse on the Temple of the Ocean King, sucking the life force of anyone who enters, unless they are in a Safe Zone or possess the Phantom Hourglass. He also created Phantoms to roam about the corridors, invincible except for boulders, trapdoors, and the Phantom Sword. Blaaz, Cyclok, and Crayk attacked the three spirits, Leaf, Neri, and Ciela. Ciela was able to escape by splitting her power into two as Oshus did, though she lost her memory and most of her power. Leaf and Neri were captured and held prisoner in the Temple of Fire and the Temple of Wind, while Ciela's other half was imprisoned in the Temple of Courage.

Bellum also created the Ghost Ship, driven by the Diabolical Cubus Sisters, to capture people for him to drain their life force, as he does to Tetra. Link, however, was able to destroy all of Bellum's servants and obtain a Phantom Sword, the only sword able to destroy him, and fought him at the bottom of the Temple of the Ocean King. Link defeated Bellum, restoring Ciela's memory and power, which she used to create Phantom Spheres. Link used the Phantom Spheres to stop time and defeat Bellum.

Bellum survived, however, and possessed the Ghost Ship. Link destroyed the Ghost Ship, but Bellum supposedly killed Oshus and tried to eat Link and Tetra. Linebeck, however, intervened, so Bellum possessed him, turning him into a giant Phantom. Though Bellum trapped Ciela with his tentacles, Link was able to make him briefly release his grip on her long enough for her to give him some Phantom Spheres, allowing him to freeze time and attack Bellum's eye on his back.

After a long battle, Link defeated Bellum, who was driven out of Linebeck and destroyed in an explosion of sand, the last of the Sand of Hours, which was absorbed into the Phantom Sword, breaking the seal on Oshus's power and returning him to his true form.

Child and Decline Timeline
Since Link and Zelda never came to the World of the Ocean King and defeated him, Bellum's conquest would have been successful and he would have destroyed Oshus and ruled the World of the Ocean King.

Powers

 * Predicting movements: Bellum knows what move you are about to make before you do it. As the Ocean King claims, "He was always a step ahead of me."
 * Earthquakes: When in rage, Bellum has been known to cause earthquakes.
 * Creating Phantoms: Phantoms are invincible monsters that can only be killed by the Phantom Sword with a back strike. Bellum has the power to spawn these monsters using life force.
 * Draining Life Force: Bellum, like his Phantoms, thrives off the life force of his victims. The Ghost Ship is used to capture sailors to use as victims. Also, anyone who enters the temple of the Ocean King(which Bellum took over) will get their life sucked out.
 * High Durability: One of the only things that are able to strike Bellum is the Phantom Sword- a combination of the three pure metals: Crimsonine, Aquanine, and Azurine, forged perfectly into a blade, with the Phantom Hourglass integrated into the hilt using powerful magic. Anything else is supposedly unable to damage Bellum other than the Master Sword, which would also affect him as it is "the blade of evil's bane".
 * Possesing: Bellum can latch itself onto a victim and turn the victim into a giant Phantom under his control, as he does to Link's friend Linebeck.

Ghost Ship
Bellum posseses his Ghost ship and makes it even more powerful than before.

Bellumbeck
Bellum possesses Linebeck and transforms him into a massive Phantom.

Trivia

 * "Bellum" is the Latin word for "war" or "battle".
 * Despite his immense power, the only moves he uses in battle before he possesses the Ghost Ship are summoning enemies, whipping Link with his tentacles, and, during the final phase of his first form, flying around in circles.