Oshus

Oshus is the Ocean King who watches over the Great Sea in Phantom Hourglass and the creator of the Phantom Hourglass. His true form is that of a large white whale, but he initially appears to Link as an old man on Mercay Island, where he helps him begin his quest by introducing him to Ciela.

Biography
At the beginning of the game, Link finds Ciela at the Mercay Island beach, and she tells him about "Grandpa", who found her and took care of her when she lost her memory. Link goes into a house near the beach and finds an old man called Oshus. Link tells him what happened, but Oshus want him to stay away from the Ghost Ship. Link says that he is not going to give up, so Oshus tells him about Linebeck, who could help him. After some time, Link steals Oshus's Sword, and Oshus teaches him how to use the sword. Once Link recovers the Spirit of Courage from the Temple of Courage, Oshus reveals that it was in fact the missing part of Ciela, because she separated herself to escape from Bellum and fuses the two.

Soon afterwards, when Link finds Tetra petrifired aboard the Ghost Ship, Oshus appears and reveals his true identity to Link and Linebeck, and explains that much of his life force was stolen by Bellum, who is using the ship to collect more victims, and that they had to help him defeating Bellum. His further revelation that there was no treasure aboard the Ghost Ship infuriates Linebeck, who refuses to continue cooperating until Oshus promises to grant him one wish. Oshus tells them about the three Pure Metals and that they can forge the Phantom Sword. Link finds the three Pure Metals and Zauz, a blacksmith, create the Phantom Blade. Oshus uses the Phantom Hourglass and creates the Phantom Sword. After Bellum is defeated and his life force is returned, Oshus reveals his true form, a white whale, grant a wish to Linebeck and send Link and Tetra to their original world. Oshus provides Link with the Oshus's Sword and Phantom Sword.

Theory
The Ocean King is the second of three flying whale creatures to appear in the series, the first being the Wind Fish in Link's Awakening and the third being Levias from The Legend of Zelda: Skyward Sword. Because of this, it has been theorized by some fans that Levias, the Wind Fish, and the Ocean King may be related, if not the same being.