Guardian

The Guardian is an enemy from Kingdom Hearts.

Ansem did not battle Sora alone in the End of the World, he used a familar Heartless known as the Guardian. It served as a shield for Ansem during the battles against Sora. It would leap from behind Ansem to block an attack. Eventually, the Guardian transformed into the World of Chaos, revealing it as Xehanort's true Heartless while Ansem was simply a puppet.

The Guardian resurfaced during Kingdom Hearts 2: Final Mix+, when Riku used the dark powers to defeat Roxas. It no longer makes an appearance after being used to subdue Roxas, as Riku, who only used the darkness as his last resort, elects not to summon it any longer for fear of darkness already eating at him.

This heartless is actually Xehanorts Heartless' true form. His body is actually Riku's only it was changed to fit his appearence when he fully controlled his body. Without it Xehanorts Heartless is only the guardian.