Crookshanks is Hermione Granger’s cat, introduced in Harry Potter and the Prisoner of Azkaban. He is described as half-Kneazle, which makes him unusually intelligent and able to sense untrustworthy people, like Peter Pettigrew disguised as Scabbers. He also quickly trusted Sirius Black in his Animagus form, showing good judgment of character.

The theory that Crookshanks might be Lily Potter reincarnated comes from fans noting how protective he is of Harry and his unusual intelligence. He was also at the Magical Menagerie for a long time before Hermione adopted him, hinting at a mysterious backstory. Still, there is no indication in the books that reincarnation—especially of a human into a magical animal—exists in the wizarding world.

So, while it’s a fun theory, it’s not supported by any canonical material. Crookshanks is simply a clever magical creature—not Lily Potter in disguise.

Would you like a list of other popular Harry Potter fan theories explored and explained?