The Patronus is one of the most powerful defensive charms in the Potterverse. The spell, which requires wizards and witches to channel positive energy, creates one of two types of Patronuses: corporeal and incorporeal, with the former being much more powerful than the latter. These spirit guardians help defend their conjuror against dark creatures, including Dementors and Lethifolds. Hidden within one's personality, a Patronus is awakened when confronted with inhuman evil—hence why we don't see Lord Voldemort and his Death Eaters running around with protective blue beasts.
Any Patronus can be used for protection, but only the most powerful corporeal Patronus can take on shape and form, offer guidance, and deliver messages to other witches and wizards. During the Battle of Hogwarts, Ernie Macmillan's Boar broke out to battle while Minerva McGonagall dispatched three corporeal cats to warn the other Heads of Houses.
Typically taking the form of the caster's favorite creature, Patronuses are unique to each conjurer's personality and strengths. Can you identify the witch or wizard based on their Patronus?