“Expecto Patronum!” A wizard shouts to conjure up a manifestation of their happiest memory in magical animal form, a spectre that can ward off against one of the deadliest enemies known — a Dementor. It’s a very difficult spell, but an important one, especially if you want to avoid the killer Dementor’s Kiss. Your patronus is also a representation of your own id, your family origins, and your own sense of happiness, so the animal that gets conjured will strongly resemble your own personal beliefs.
“They’re not supposed to be pretty,” Harry says. “They’re supposed to protect you.”
Harry Potter’s own patronus is a stag, just like his father, James, who could also transform himself into a stag. Deer are closely associated with compassion, peace, and as a guiding light — all things Harry aspires to be, and traits he’s often told his dead parents have. Hermione is an otter, a fitting bright and overeager animal, while Ron’s is a Jack Russell terrier, a small, anxious but loyal dog.
“Your father is alive in you, Harry, and shows himself most plainly when you need of him,” Lupin says. “How else could you produce that particular Patronus? Prongs rode again last night.”
It seems fitting that people would feel drawn to get their own interpretation of their patronus, much like wands, dark marks, and sorting hats. And everyone has a broad idea of what sort of patronus they’d have — we’ve seen Pikachu, tons of cats, a few dogs, and plenty of deer. Much like other tattoo talismen, the patronus has become a way to show your own spirit animal as well as your love for the highly regarded series.