Patronus Charm

"A Patronus is a kind of positive force, and for the wizard who can conjure one, it works something like a shield, with the Dementor feeding on it, rather than him. In order for it to work, you need to think of a memory. Not just any memory, a very happy memory, a very powerful memory… Allow it to fill you up…lose yourself in it…then speak the incantation ‘Expecto Patronum’."

- Remus Lupin teaching Harry Potter the Patronus Charm

A Patronus is an insubstantial animal form protector created by the advanced Patronus Charm spell, and one way to defend against Dementors and certain other Dark creatures. The spell requires the use of a wand, concentration on a powerfully happy memory, and the incantation "Expecto Patronum". Presumably, specific physical gestures with the wand are also required, but they are not mentioned specifically. The Patronus Charm is advanced magic and difficult to master, especially in emotionally difficult circumstances.

Form
There are some whose Patronus is fully formed (corporeal), taking the shape of fairly solid-looking animals; the Patronus of some also appear only as a wisp of silvery mist. It is a very complex charm and many qualified wizards have trouble with it. Harry Potter is one of the youngest known wizards to cast a Patronus; he was taught how do so in 1993 at the age of thirteen by Remus Lupin. In a Dumbledore's Army lesson, Harry taught the members to use the charm. Some were even successful in casting a corporeal form, though Harry said this might be because there was no Dementor to make them frightened, although some members were later shown to be able to use corporeal Patronuses in the presence of Dementors.

The Patronus Charm, like Animagus forms, has been said to reflect the personality or feelings of the witch or wizard. They are, however, subject to change if the caster goes through an emotional change of some sort. For example, Nymphadora Tonks's Patronus changed from its previous form to that of a werewolf, reflecting her love of Remus Lupin, a werewolf. Another example is Severus Snape, whose Patronus was that of a doe, the same as Lily Evans, though this may have been the case all along rather than a change from its original form, as Snape was in love with Lily for most of his life. If a wizard is an Animagus and can summon a corporeal Patronus, the two may take the same form, as this was the case for Minerva McGonagall and James Potter.

The Charm
"Make it a powerful memory, the happiest you can remember. Allow it to fill you up… Just remember, your Patronus can only protect you as long as you stay focused… Think of the happiest thing you can."

- Harry Potter teaching the Patronus Charm to Dumbledore's Army

In order to cast this charm, one must think of an extremely happy memory or idea, and then say the incantation: "Expecto Patronum". Because of this, negative emotions can compromise a wizard or witch's ability to cast a Patronus. For instance, Harry Potter, Ron Weasley, and Hermione Granger all had difficulty casting their Patronuses when under the negative influence of Salazar Slytherin's locket, one of Lord Voldemort's Horcruxes, and after witnessing the death of Fred Weasley in battle.

Uses
There are two known uses for the Patronus charm. The first use of The Patronus is that it can be used to drive off certain Dark creatures such as Dementors and Lethifolds, and is the only known charm that will work against them.

The other use was devised by none other than Albus Dumbledore, who invented a way of using the Patronus to deliver messages. This source of communication is believed to be exclusive to the members of the Order of the Phoenix. Using the Patronus for communication offers great advantages in security, as Patronuses identify the caster and are Dark-proof.

Etymology
Patronus means "protector" or "guardian" in Latin, reflecting the role the Patronus Charm plays. In archaic Latin, it meant "father", which is interesting, considering that Harry Potter's Patronus is the same as his father's Patronus and Animagus form. The Latin word exspecto or expecto means "I watch for" or "I await", thus the charm's incantation roughly translates into "I await a protector".

The Patronus in the films
In the film adaptation of Harry Potter and the Prisoner of Azkaban, Harry's non-corporeal Patronus is more like a shield. In addition, his corporeal Patronus, a stag, sent out a sort of omni-directional pulse, which drove the Dementors away, rather than running them down (likely because of the number of Dementors and their flight abilities in the film). In Harry Potter and the Order of the Phoenix (film), his Patronus physically attacks the Dementors as in the books.

Behind the scenes

 * In the first chapter of Harry Potter and the Deathly Hallows, a white peacock appears in the gardens of Malfoy Manor. Some fans believed this bird to be Lucius Malfoy´s Patronus. However, Joanne K. Rowling stated that no Death Eater except Severus Snape could conjure a Patronus. This means that the peacock was in fact a living creature.


 * In video game adaptation of Prisoner of Azkaban, Expecto Patronum is a jet of light (before casted, a white ring goes up Harry's arm and if it reaches top of the wand, Harry has to try the spell again) and is used only to attack Dementors. Only once a stag (Harry's Patronus) jumps out of the wand and kills all the Dementors nearby.

Appearances

 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Prisoner of Azkaban (film)
 * Harry Potter and the Prisoner of Azkaban (video game)
 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows

Notes and references
Patronus Patronus thumb|300px|right