Vaati

The villain in the Four Swords subseries of the Zelda games, and the The Legend of Zelda: The Minish Cap. Vaati is a Wind Mage, and is seen taking on two main forms, one a human, the other a monster (much like Ganon and Ganondorf). In the game The Minish Cap, Vaati also has a third form between his human and true demon form, namely that of a humanoid demon sorcerer.

In Four Swords
Released from his prison within the Four Swords, Vaati kidnapped Princess Zelda, forcing Link to go off and search for the princess. After travelling over three different lands and the dungeons they contained, Link and his three other selves confronted the wind mage in the Wind Palace, the seat of Vaati's power. After a arduous battle between the sorcerer and the heroes, Link was able to reseal Vaati into the Four Swords blade.

In Four Swords Adventures
After Link had rescued Zelda and sealed Vaati in the Four Swords, Hyrule was at peace for a time. This changed when Ganondorf stole the Dark Mirror from the Temple of Darkness. Creating Shadow Link to kidnap Zelda and the Shrine Maidens, Ganondorf tricked Link into releasing the Four Sword, unsealing Vaati in the process. During his adventure to save Hyrule, Link found out that Vaati was not the real enemy. Instead, Ganondorf had instigated the ordeal with Vaati to distract Link, allowing Ganondorf the time needed to steal the Dark Trident. With this, he would transform into the dread demon Ganon, taking over Hyrule in the process. Over the course of the adventure, Link rescued the Shrine Maidens and Zelda, and restored his good name upon defeating Shadow Link with Zelda's help. At the final battle, Link and his split selves defeated Vaati, and sealed Ganon within the Four Swords with the help of Zelda and the Shrine Maidens. With this, peace returned to Hyrule, and the Four Swords was layed to rest in its shrine. With this being the last tale in the Four Swords era, Vaati was suppossedly finally beaten in this game. He met his end when Ganon, no longer needing him disposed of the wind mage. Wether he actually destroyed Vaati, or merely sealed him inside the Dark World, is unknown.

In The Minish Cap
The origin tale of Vaati is told in the adventures that Link faced with the Minish Cap. Originally of the Minish race, Vaati was fascinated by the evil that could come from the heart of man. When his master, Ezlo, fashioned a powerful cap as a gift for the humans, Vaati stole the cap and transformed his master, so that he would not stop him. Then, taking human form, Vaati set out to find the means to allow him to become the greatest sorcerer the world had ever seen. He found that means in the legends of the Light Force, a mystical magic said to bestow upon the wielder the powers of godhood. Over the course of the game, Vaati continuously sought its location, finding it in the end in the most unlikely of places. In this game, Vaati has four forms, a human form, a demon sorcerer, a wind mage and finally, a true demon form.