In “How the Grinch Stole Christmas!”, the Grinch disguises himself as Santa Claus.
On Christmas Eve, the Grinch creates a red Santa suit and uses it to sneak into the homes of the Whos while they sleep. His disguise lets him pretend that he is collecting decorations and presents for delivery, even when Cindy Lou Who catches him near her family’s Christmas tree. His dog, Max, completes the deception by dressing as a reindeer.
The disguise is part of the story’s central reversal: instead of delivering gifts, the Grinch steals them. The 1957 book, the 1966 animated television special, and later screen adaptations all retain this basic plot device. A common mix-up is identifying Max as the disguised character; Max is dressed as a reindeer, while the Grinch himself poses as Santa Claus.