Zero is a ghostly dog that appears to be made of a white sheet, much like a stereotypical ghost. Like Pluto, he has basset hound-esque floppy ears. His "eyes" are just empty holes in the sheet. Zero's snout is very long and thin, and his upper jaw curls upward at the tip. His nose is a small jack-o-lantern, and his collar is a faded brown color. In Kingdom Hearts 358/2 Days, Zero appears to be a light blue as compared to his usual white appearance.
Zero had a relatively small role in Kingdom Hearts, appearing only as a ghostly hallucination.
- "So that floating doggy thing can sniff out Heartless?"
- —Roxas admiring Zero's Heartless-sensing capabilities
When Roxas finds Jack and Zero in the Graveyard, he is amused to see that the ghostly dog can sense the Heartless's presence around him with his nose.
Showing Jack a Carrier Ghost that was hiding in a balloon, Zero is rewarded by a happy Jack while Roxas looks on. Roxas realizes that if he gives Zero a bone, the dog would reveal the Heartless' hiding places. Zero gladly complies, and Roxas completes his missions with ease.
Zero first appeared in the 1993 movie The Nightmare Before Christmas. In the movie, Jack finds the door to Christmas Town while he is taking Zero for a walk. Later, when Jack wants to take off through the thick fog to deliver presents, Zero has to light the way. At the end of the movie, Jack and Sally kiss each other as Zero looks at them. He then flies into the air and transforms into a star.
- Unlike in past games, Zero's movement in Kingdom Hearts 358/2 Days is represented by the sound of blowing wind.
- When you run up to Zero in Kingdom Hearts, he would disappear and you would go right through him, while he was able to interact with Sora in Kingdom Hearts II.