Jalhalla

Jalhalla is the immense, obese leader of all Poes and ghosts who appears in The Wind Waker and Four Swords Adventures.

The Wind Waker
Jalhalla resides in the core of the Earth Temple, and is responsible for the death of the Earth Sage, Laruto. He owes his existence to a small group of about twelve normal poes, and a mask that uses their power to form Jalhalla. This beast must be brought down in order to partly restore power to the Master Sword, by placing Medli in her new position as the Earth Sage.

Strategy
The trick to bringing him down is to direct light at Jalhalla with the Mirror Shield, causing him to materialize and fall. Link must then lift the giant off the floor with the Power Bracelets and throw him, causing him to roll into one of the purple columns of spikes on the walls. This will cause his body to split into many Poes for the young hero to dispose of. To make the task easier, Link can use the Hurricane Spin technique (if it's learned already) to quicken the job (only five Poes can be killed at any time, however). Link repeats this process to destroy all the Poes by any means to destroy Jalhalla. The boss's mask then appears, and dumbfounded that there are no more Poes to use, he tries to escape when a beam of light stops this attempt by solidifying him, numbing him, and causing him to crash into the floor and shattering. Link is then rewarded with a Heart Container and a more powerful Master Sword.

He is found again in Ganon's Tower later in the game. He is defeated for a second time (in the same fashion) to break the seal to the door leading to Ganondorf.

Nintendo Gallery figurine description:
 Jalhalla, Protector of the Seal  Habitat: Earth Temple Underlings: Poes This gigantic ghost rules over all Poes. After reflecting light onto it with the Mirror Shield, you can lift it and throw it around.

Four Swords Adventures
Jalhalla also makes an appearance in Four Swords Adventures during the stage Near the Fields, as the boss of both The Swamp and during the Infiltration of Hyrule Castle.

Trivia

 * Jalhalla's name may be a play on Valhalla, a kind of warrior's heaven in Norse mythology. His name also sounds similar to Jahannam, the name of the Islamic equivalent of Hell.