Severus Snape's doe Patronus in Harry Potter revealed that he had been in love with Lily Potter and was the one who helped Harry find the Sword of Gryffindor, but its meaning went far deeper than ...

The backstory of Severus Snape's doe Patronus came from his feelings for Lily Potter. Similarly to Tonks' love for Lupin, Snape's Patronus became representative of the person he was infatuated with.