Zero

Zero is Jack Skellington's ghost dog. He originally appeared in Tim Burton's "The Nightmare Before Christmas".

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