Animagus

"Please, sir. An Animagus is a wizard who elects to turn into an animal. A werewolf has no choice in the matter."

- Hermione Granger discussing the differences between an Animagus and a werewolf

An Animagus (pl. Animagi) is a witch or wizard who can morph him- or herself into an animal at will. It is a learned, rather than hereditary skill, unlike those of a Metamorphmagus. Information on Animagi is taught to Hogwarts students during their third year Transfiguration class.

Acquiring the skill
Only very powerful and skilled wizards and witches are able to become Animagi. The process of becoming an Animagus is long and arduous, and has the potential to backfire and cause the transformation to go horribly wrong. Once the initial training is over, an Animagus can change at will, with or without a wand.

Animagi can only take on the form of one specific animal. This animal form is not chosen by the wizard, but determined by their personality and inner traits. It may also be that the full-bodied patronus may reveal what a witch or wizard would turn into if they were an animagus. An example, we find in the 7th book when Professor McGonagal, a known cat animagus also has the patronus of a cat. Apparently, the form the patronus takes may be determined by the same inner-traits as the animagus form. It can be conjectured that James Potter's patronus was a stag, as he took that form when he transformed. His wife's patronus was a doe. The only doubt about this theory is that Animagi seem to retain the same sex as the human form, whereas Severus Snape's patronus is a doe because of his love of Lily Potter. It therefore might differ somewhat between patronus and Animagi forms. It is unknown whether Animagi can take the form of a more "magical" creature. An Animagus in animal form is also not restrained by the lifespan limit of the creature that they otherwise transform into, seen in the case of Wormtail, who stayed in the form of a rat for at least twelve years, remaining alive despite the fact that rodents have a short lifespan.

Each Animagus bears an identifying mark on their animal form that is caused by something on their human body. This may be a physical trait like dental structure, or an acquired trait such as glasses. For example, both Minerva McGonagall and Rita Skeeter have markings on their Animagus forms caused by their spectacles, and Peter Pettigrew had a bald spot on his Animagus form from his balding head. If an Animagus undergoes a major physical change, such as the loss of a limb, their animal form will also reflect that, as in the case of Peter Pettigrew's finger.

In addition, an Animagus will appear to lose their clothing upon morphing. The clothing will reappear upon re-establishing the human form. What physically happens to the clothing is unknown. A strong possibility, however, is that the clothing is enchanted beforehand, and will morph/disappear with the person as they do so. An example is when Peter Pettigrew morphs into a rat whilst Sirius Black and Severus Snape are occupied detaining the werewolf Remus Lupin. Another explanation would be if the clothes themselves are physically involved in the morphing, i.e. transforming into the skin and fur of the animal form.

Transfiguration vs. Animagus transformation
The difference between Transfiguration and the Animagus transformation ability is that an Animagus can change into an animal whenever they want, without a wand or an incantation. Being an Animagus is an ability, and Transfiguring requires a spell. An Animagus still thinks as a human does when they are in their animal form, seeing as Rita Skeeter was able to eavesdrop on others' conversations when she was in the form of a beetle. However, an Animagus's feelings are not as complex when they are in their animal form.

Animagi also has the ability to communicate with normal animals. There seems to be a clear understanding of want and need in this ability, but the full extent and quality is unknown. Sirius Black's Animagus form, a black dog named Padfoot or Snuffles (as nicknamed by Harry, Ron, and Hermione), was able to communicate on a rudimentary level with Crookshanks, Hermione Granger's part-kneazle cat. The precise form of communication is yet unknown, though it is probably not telepathy since Sirius did not know Crookshanks' name until Hermione told him. As well, Peter Pettigrew picked up hints and directions from passing rats as he traveled around Albania in search of Voldemort.

There is a particular spell which creates a blue and white flash that will force an Animagus out of their animal form. Remus Lupin and Sirius Black once used it to force Peter Pettigrew out of his rat form. This spell could possibly be the Homorphus Charm that Gilderoy Lockhart claims he used on the Wagga Wagga Werewolf to force him into his human form.

It is also important to note that a werewolf is fundamentally different from Animagi. Lycanthropy is caused by a blood infection transmitted through the bite of a werewolf, whereas the Animagus skill is learned. The werewolves cannot keep their minds after a transformation (unless they take the Wolfsbane Potion), nor can they control themselves when they transform, while Animagi can do both. However, as werewolves only harm humans, Animagi, while in their animal forms, are safe to be in the company of werewolves.

Wizarding law
"Rita Skeeter isn't going to be writing anything at all for a while. Not unless she wants me to spill the beans on her... I found out how she was listening in on private conversations when she wasn't supposed to be coming into the grounds... Rita Skeeter is an unregistered Animagus. She can turn into a beetle... I've told her she’s to keep her quill to herself for a whole year. See if she can't break the habit of writing horrible lies about people."

- Hermione Granger on her blackmail of Rita Skeeter.

Every Animagus is required to register with the Ministry of Magic at the Improper Use of Magic Office. This registration includes revealing one's animal form and one's distinguishing markings. The register is available to the public. The primary reason for registration is to ensure the Animagi do not abuse their abilities, as the Ministry is able to keep track of them. One example is because Sirius Black is an unregistered Animagus, he was able to use his form to escape from Azkaban, as the Ministry did not take this into account when imprisoning him.

The penalty for failing to register as an Animagus is a sentence in Azkaban, though the length of time is unknown. Rita Skeeter gave up an entire year of writing articles, her main means of livelihood, so that Hermione Granger would not turn her in as unregistered, and consented to writing an article free of charge at Hermione's request. That suggests either a rather lengthy sentence, or the fact that being sent to Azkaban for any length of time is a considerably bad punishment to begin with.

Due to the complexity of the magic involved in becoming an Animagus, they have become very rare. There were a total of seven registered Animagi in the twentieth century. It is also partially because of this complexity that Animagi are required to register themselves.

Known Animagi

 * Falco Aesalon — Falcon; the first recorded Animagus; the registration system was not in existence in his time.
 * Morgan le Fay — Bird; the registration system was not in existence in her time.
 * Cliodna — Sea bird; the registration system was not in existence in her time
 * Minerva McGonagall — Tabby cat; registered.
 * James Potter — Large stag; unregistered.
 * Sirius Black — Large black dog; unregistered.
 * Peter Pettigrew — Rat; unregistered.
 * Rita Skeeter — Beetle; unregistered.
 * Unidentified witch — Cat; registered.
 * Babbitty — Fictional character. Rabbit

Etymology
Combination of the word "animal" and the Latin word "magus", meaning "animal wizard".

Behind the scenes

 * J. K. Rowling has stated that she would fancy an otter — her favourite animal — as her Animagus form, though if she actually transformed, she suspects she might be "a guinea pig or something, which would be quite embarrassing."
 * J. K. Rowling once joked that Godric Gryffindor was actually the Giant Squid in the Hogwarts lake.
 * According to W.O.M.B.A.T., an Animagus transformation is two of the following: a kind of Self-Transfiguration, a kind of Self-Charm, or a kind of magic that is neither Transfiguration nor Charm. You are asked to pick the statement that is incorrect. This would mean Animagus transformation is either a kind of Self-Tranfiguration but not actually a Transfiguration or Charm spell, a kind of Self-Charm but not actually a Transfiguration or Charm spell, or a kind of Self-Transfiguration and Charm spell.
 * In the film adaptation of Harry Potter and the Prisoner of Azkaban, Peter Pettigrew is fully clothed when he transforms to his human form in the Shrieking Shack, but later, when he transforms to a rat, he leaves his clothes behind.
 * Also in the film adaptation of Harry Potter and the Prisoner of Azkaban Sirius's Animagus form is a large tough looking dog but in Order of Phoenix he looks more like a kind harmless dog. It could be that he fixed his appearances.
 * An Animagus does not know what his or her animal form will be prior to the transformation.
 * Interestingly, the first three known animagi prior to the registration system all took the form of birds (Falco Aesalon, Morgan le Fey and Cliodna). The two known registered animagi both become cats (Minerva McGonagall and an unknown witch).

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Philosopher's Stone (video game)
 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Chamber of Secrets (video game)
 * 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 Goblet of Fire (film)
 * 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 Half-Blood Prince (film)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1 
 * Harry Potter and the Deathly Hallows: Part 2 
 * LEGO Harry Potter: Building the Magical World
 * LEGO Harry Potter: Characters of the Magical World
 * LEGO Harry Potter: Years 1-4
 * LEGO Harry Potter: Years 5-7
 * Pottermore
 * Harry Potter LEGO Sets