Levias

Levias is a wise, whale-like Sky Spirit in Skyward Sword. He has served as the protector of the skies for ages and lives in the Thunderhead. Levias has a particular fondness for Pumm's pumpkin soup, which Pumm always offered on a sky isle that had a perpetual rainbow above it, before the Thunderhead engulfed it.

Biography
Before the goddess Hylia transferred her soul into the body of a mortal, she appointed Levias as the guardian of the skies. She also left the Sky Spirit a hint as to the location of the Triforce, which was one of the four parts of the "Song of the Hero", a melody that would unlock the final trial for the chosen hero. However, at one point, Levias was corrupted by evil forces and became plagued with parasitic eye-like appendages, possessing him and causing him to attack anyone who comes near.

After learning of Levias from the Headmaster Gaepora, Link speaks to Owlan and learns that although Levias can be found in the Thunderhead, he has become possessed by Bilocyte and will not listen to reason. He tells the young hero to talk to Pumm, who makes annual Pumpkin Soup offerings to Levias. Link uses this knowledge to his advantage and places a basin of Pumpkin Soup in an island of the Thunderhead to lure the beast out of the cloud sea and, with the aid of his Loftwing and the newly-learned technique Spiral Charge, removes the parasites. Upon the removal of the last visible parasite, a Bilocyte occupying Levias' blowhole emerges. Link removes this parasite as well, and upon hearing that Link was searching for the Triforce, Levias informs him of the four parts of the "Song of the Hero" is needed to find the Triforce. Levias then instructs Link to track down the three surface dragons, Faron, Lanayru, and Eldin, to learn their parts of the melody. Once he has done this, Levias imparts the final part of the "Song of the Hero" to Link.

Theory
Levias is the second flying whale creature to appear in the series, the first being the Wind Fish in Link's Awakening. If this relation is to be believed, it can be inferred that either:

A) The Wind Fish is a descendant of Levias.

B) The Wind Fish and Levias co-exist even during the time of "Skyward Sword", but that is not revealed. It is known though, that both are possibly eternal beings, so that may be possible.

C) Levias is the Wind Fish. It is hinted that Levias has infinite knowledge and possibly powers to create things, and in the far future, Levias creates Koholint.

Etymology
Levias' name is derived from Leviathan, a mythological monster from Biblical text (Job 41). Fittingly, in modern Hebrew, "Leviathan" means "whale."