Snape's doe Patronus reveals his one true motivation throughout Harry's life: to protect the child of the woman he loved.

In "Deathly Hallows," Snape also uses his Patronus to help Harry on his quest to find Voldemort's horcruxes; a Patronus charm can be used to send messages, and Harry seems to subconsciously recognize the doe as an extension of his mother, allowing him to trust it.

According to J. K. Rowling, the author of the ' Harry Potter ' series, Snape was the only Death Eater who could conjure a Patronus charm at all.

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