Zero

Zero is Jack Skellington's pet ghost dog from Kingdom Hearts and Kingdom Hearts II''. He originally appeared in Tim Burton's "The Nightmare Before Christmas". He will appear in Kingdom Hearts 358/2 Days alongside Jack.

Kingdom Hearts
''Jack's ghost dog. He comes out of his grave whenever Jack calls. He's very loyal to his master and loves it when Jack plays with him.''

He loyally followed Jack in "Tim Burton's The Nightmare Before Christmas" (1993).

Kingdom Hearts II
The Nightmare Before Christmas (1993)

''Jack's ghost dog. He comes out of his grave whenever Jack calls, and never gets tired of playing fetch with his master.''