In the Harry Potter universe, the Patronus Charm is one of the most significant spells. As explained in Harry Potter and the Prisoner of Azkaban, the Charm is used to defend individuals against evil forces, particularly Dementors. While it is incredibly challenging to conjure a full-bodied Patronus, when successfully cast, a Patronus will often appear in the form of a silver animal. The animal which appears varies according to the individual personality of the witch or wizard who summons it.