Even though Expelliarmus, the Disarming Charm, goes on to become the trademark spell of Harry Potter, he is also known for mastering the ancient and notoriously difficult Patronus Charm. In the spell’s most powerful form, the wisps of silver become a full-bodied creature that is specific to the wizard or witch who conjures it. Channeling the positive emotions of the caster, it acts as his or her spirit guardian.
According to J. K. Rowling, there is a wizarding legend that a young man called Illyius had cast the Patronus Charm when his village was under attack by a dark wizard named Raczidian and his army of Dementors. Although his Patronus was just a small mouse, its bright glow caused the Dementors to flee. Raczidian also attempted to cast the spell in response, but maggots shot out of his wand instead, which crawled up his body and devoured him. This is meant to show that a Patronus is the embodiment of purity, and is often associated with those who are fighting for a noble cause.
What Is the Patronus Spell?
The Patronus Charm is widely regarded as being “ridiculously advanced”, much beyond N.E.W.T.-level. Even many qualified wizards and witches have trouble casting the complex spell. Harry, who learns the spell at the age of 13 only, is actually one of the youngest wizards who has been able to achieve this feat.
As Lupin teaches Harry in Harry Potter and the Prisoner of Azkaban, one has to solely focus on the happiest possible memory they can think of to successfully cast the spell. The happier it is, the more likely it is that the charm would work. A person can also imagine a possible scenario that could serve as a happy memory. This is demonstrated by Harry when he is taking his Defense Against the Dark Arts O.W.L. — he imagines Umbridge getting sacked as the Headmistress, and impresses his examiner with a full-fledged Patronus as a result.
The next step is to draw circles with one’s wand to increase the intensity of the spell. After that, they should say the incantation ‘Expecto Patronum’ for the Patronus to emerge from the tip of their wand.
Since the charm is a projection of the caster’s most positive feelings, it can be difficult to perform the spell under dire circumstances. When Harry teaches the spell to the members of Dumbledore's Army, some of them manage to succeed in casting it, but Harry reminds them that this might not be so in the real world when they are confronted by actual Dementors. In Harry Potter and the Deathly Hallows, when the Golden Trio breaks into the Ministry of Magic and ends up being chased by Dementors, Hermione has trouble mustering a happy memory (and understandably so). During the Battle of Hogwarts, the three of them come across Voldemort’s Dementors but cannot summon the will to cast the charm. Even Harry, after witnessing Fred’s death, initially allows himself to be pulled into the oblivion that comes with the Dementor’s Kiss before being rescued by Luna, Seamus and Ernie.
A Patronus can be in two forms: non-corporeal, when it can appear as a “shapeless cloud of mist”; and corporeal, when it has a clearly defined shape with distinguishing features. Only a highly skilled wizard or witch is able to produce a corporeal Patronus. Incorporeal Patronus are considered just a pale imitation in comparison, and are not as effective either. However, being able to summon an incorporeal Patronus is still regarded as an impressive accomplishment.
What Is a Patronus?
The Patronus Charm is primarily used to ward off Dementors and, as seen in Fantastic Beasts and Where to Find Them, Lethifolds. A Patronus represents hope and happiness — what a Dementor essentially feeds upon — and cannot feel any negative emotions. This is why it is not affected by the Dementors and is able to act as a shield against them, when they attempt to make the caster relive their worst memory. A notable example is when Harry is able to drive away over a hundred Dementors when they surround him and Sirius at the Black Lake of Hogwarts. He again manages to save himself and his cousin Dudley from another Dementor attack in Harry Potter and the Order of Phoenix. The spell is also used just before the Battle of Hogwarts, when the professors and students are casting protective charms around the castle.
A Patronus can also be used as a means of communication, as shown by Kingsley, when his Patronus warns that Voldemort has taken over the Ministry; Arthur, when his Patronus reassures Harry, Ron and Hermione that everyone is safe after the Death Eater attack at Bill and Fleur’s wedding; and McGonagall, when she conjures three corporeal Patronuses to inform the other Heads of Houses about the impending Battle of Hogwarts. Snape also conjures his Patronus to lead Harry to the sword of Gryffindor in the Forest of Dean.
Why Does a Patronus Take Different Forms?
When a witch or wizard is able to produce a fully-formed Patronus, it takes the shape of a glowing, silvery creature with which the caster has a strong affinity. The animal is unique to each individual, reflecting their innermost nature. For instance, Harry’s Patronus is a stag, which happens to be his father’s Animagus form. Considered the protector of animals, it symbolizes leadership and bravery, both of which are his character’s core qualities. Hermione’s Patronus is an otter, which is a curious and clever creature. Similarly, Ron’s Patronus is a Jack Russell terrier — a fitting animal since it is also loyal and stubborn like him. Interestingly, Jack Russell terriers are particularly fond of chasing otters – hence, establishing a connection between him and Hermione.
However, it is also possible for one to disguise their Patronus. This is illustrated when Lupin, a werewolf, chooses to produce an incorporeal Patronus as he feels the actual one (that takes the form of a wolf) would reveal his true identity. It may be that a Patronus can also represent the Animagus form of a wizard or witch — as proven in the cases of James and McGonagall (whose Patronus is a cat).
It can also change when one experiences extreme emotions or changes in their life. Snape’s Patronus famously changes to a doe, which happens to be Lily’s Patronus — thus, signifying his love for her. Tonks’ Patronus also goes from being a rabbit to a wolf, because she has fallen in love with Lupin. Rowling has also stated that it is common for a Patronus to “take the image of the love of one's life” as they are the ‘happy memory’ that produces it in the first place. This can also be why James’ Patronus is a stag and Lily’s is a doe.