Majora

Majora is the implied name of the entity which inhabits Majora's Mask in The Legend of Zelda: Majora's Mask. It serves as the game's main antagonist and is arguably the series' most depraved and bizarre villain. Despite appearing as an inanimate object, and using Skull Kid as its puppet, the mask carries obvious sentience and the ability to speak coherently, through its wearer or of its own power.

History
The mask was said to be used by an ancient tribe for hexing rituals, but due to the spite they poured into it, it soon became too dangerous. The tribe decided to seal it away, never to be found again. It was refound by the Happy Mask Salesman who was then robbed of it by Skull Kid. Majora takes control of Skull Kid through the mask, manipulating him to crash the moon into Termina thus killing everyone, as it is said that the mask amplifies your darkest desires. At the end of the game, Majora knocks out Skull Kid when the Four Giants arrive and flees to the moon. Majora incarnates itself into a humanoid form and serves as the game's finale.

Characteristics
The entity that inhabits the mask seems to be highly disturbed, insane, and childish. After speaking for itself for the first time near the end of the game, it declares Skull Kid was merely its puppet, suggesting that it was in fact the mask's essense itself that craved so much misery and destruction. All of the powers it used seem to suggest or induce insanity, such as the turning of Kafei into a child mere days before his wedding, the transformation of Link into a Deku Scrub, and various other bizzare and psychopathic problems it caused. The hideous visage it gave to the moon also seems to indicate madness. Inside the moon, in a very peaceful but surreal meadow, Majora (and the other 4 masks) take on the form of children, Majora sitting alone and staring at the ground. It asks Link to play a game of "Good Guys and Bad Guys", where Link is the "Bad Guy". In combat, Majora has a tendency to laugh to itself, manically, and lets out a high-pitched, childish shriek when injured, and all of his forms have a very chaotic and unsettling appearance.

Majora seems to have a strained background with the Fierce Diety. When asking to play their game of "Good Guys and Bad Guys", Majora freely offers Link the Fierce Deity's Mask so that he may become the "True Bad Guy". This, coupled with Majora's obvious sensitivity to the Deity's powers, suggests that Majora has a negative relationship with the being and wants to destroy him, or at least his incarnation. However, this was never fully elaborated upon in the game, so the nature of the two's relationship is speculatory. However, Majora's psychosis is only further evidenced by the offering of an item obviously beyond his own power level.

Majora is somewhat implied to be a woman, with characteristics like the feminine voice and antics, and the fact that the eyes of the mask somewhat resemble breasts in the Wrath form. However, high-pitched voices are often associated with insanity as well, and Majora's muscular structure appears masculine.

Battle

 * Majora's Mask
 * Majora's Incarnation
 * Majora's Wrath

Motives
Majora is the only Zelda antagonist who does not seem to have clear motives. Most villians, such as Ganon or Zant wish to rule their land, but Majora seems happy with destruction. As it amplifies the wearer's dark desires, the motive for each owner may be different. However, Majora itself most likely has differing motives from the wearer, corrupting their mind and bringing about its own ends for destruction. It seems to have a very pronounced sadistic streak, not only causing destruction but causing Skull Kid to use the mask's powers to generally make the lives of Termina's inhabitants miserable.

In the manga
Majora played the same role in the Manga version of the game, and it displayed more of personality then it did the game. For the most part it stays with the Skull Kid, but eventually abandons him when the giants stop the moon like in the video game. However, Majora mocks the Skull Kid, calling him trash and tries to kill him just because it thought he was no-fun. Link saves the Skull Kid (having grown sympathetic to him), and Majora challenges Link to a game of "tag," and gives him the Fierce Deity's Mask. Link puts on the mask and follows Majora. In the battle, Majora first just runs around, but then attacks Link, but quickly proves no-match for Link with Fierce Deity's Mask, whom effortlessly kills Majora in one attack. Majora in the manga displayed a sinister, childish personality. It appears to like to play, but its ideas of what is fun are twisted, and it even calls Link mean when he starts to defend himself.