Cheshire Cat

The Cheshire Cat is a pink and purple cat from Wonderland with mysterious powers and constantly teleports from one place to another. He speaks in riddles and wears an almost permanent grin on his face.

Kingdom Hearts
In the first game, this cat aided Sora, but his true allegiances were unknown. He appeared to summon the Trickmaster, which the cat called "Shadow", and after defeating it the Chesire Cat reveals to them that Alice was taken away by the Heartless into the shadows. It was revealed in the manga that the prank-playing cat was approached by Maleficent but he rejected her offer. Maleficent then saw him as a threat, especially after he gave Sora the ability to use Blizzard magic to destroy the Trickmaster.

Kingdom Hearts:Chain of Memories
The Cheshire Cat appears as one of Sora's Wonderland memories, giving him advice on how to save himself from being executed by the Queen of Hearts (albeit in riddles).

Kingdom Hearts: Chain of Memories
"A mysterious, grinning cat who always talks in riddles. He appears when you least expect it, and disappears whenever he pleases."

Quotes

 * "Shadows here, shadows there, shadows everywhere, and the mome raths outgrabe!"
 * "The shadows are coming! Are you prepared for the worst? If not, too bad!"

Trivia
Although not a villain in the game.The Kingdom Hearts manga implies that the Cheshire Cat was offered a position among the Disney villains by Maleficent, but according to Jafar he refused.