Werewolf

"You have only ever seen me amongst the Order, or under Dumbledore's protection at Hogwarts! You don't know how most of the wizarding world sees creatures like me! When they know of my affliction, they can barely talk to me!"

- Werewolf Remus Lupin on how he is treated because of his condition

A werewolf is a human who, upon the rising of the full moon, turns into a fearsome near-wolf. Werewolves can be distinguished from regular wolves by several small distinguishing characteristics, such as the pupils of the eyes, snout shape, and tufted tail. At all other times, they appear as normal humans, though will often seem to be ill as the full moon approaches. This condition is caused by infection with lycanthropy, usually occurring when a human is bitten by a transformed werewolf. There is no known cure, but the effects can be lessened with the Wolfsbane Potion.

Infection
"I did not know, for a very long time, the identity of the werewolf who had attacked me; I even felt pity for him, thinking that he had had no control, knowing by then how it felt to transform."

- Remus Lupin

Lycanthropy is a magical illness known to be spread by saliva-blood contact; thus, a human bitten by a werewolf in wolf form will become a werewolf him or herself. This is what happened to Remus Lupin, who was bitten as a child by Fenrir Greyback in retaliation for Remus's father offending the werewolf. However, if a human is bitten by a werewolf in human form, the victim will only acquire some lupine tendencies. For example, Bill Weasley retained scars and a craving for very rare meat after being attacked by a non-transformed Greyback.

Werewolves seldom have children, so Remus Lupin did not know whether or not his unborn son would inherit his condition but feared that it would be the case. Ted Lupin ultimately proved not to be a werewolf, however.

It seems that werewolves, when in their animal state, pose the danger of biting or killing the nearest human being. An example of this can be seen when Remus Lupin, having forgotten to take his potion in 1994, began to transform. Sirius Black instinctively changed into his Animagus dog form to launch a pre-emptive attack on Lupin whom he seemed to realise as an immediate threat to Harry, Ron, and Hermione. Lupin's now werewolf mind prevented him from recognising Sirius and the three students as his friends, and so would almost certainly have hurt them without Sirius's intervention. The latter, whilst in his Animagus form, was not at risk of being infected with lycanthropy due to the fact that humans are the only species known to be capable of infection.

Monthly transformations
"There was a terrible snarling noise. Lupin's head was lengthening. So was his body. His shoulders were hunching. Hair was sprouting visibly on his face and hands, which were curling into clawed paws."

- Description of Remus Lupin transforming

On every full moon, a werewolf will go through an incredibly painful transformation from a human into a wolf-like creature. They lose the ability to think in a human way, becoming highly aggressive towards humans, even those to whom they are close. Though werewolves usually only infect their victims through biting, they sometimes take it too far and kill their victims.

Without any humans nearby to attack, or other animals to occupy it, the werewolf will attack itself out of frustration. This leaves many werewolves such as Remus Lupin with self-inflicted scars and prematurely aged from the difficult transformations.

Treatments
Unfortunately, there is no cure for lycanthropy. However, some of the worst effects can be mitigated by consuming Wolfsbane Potion, which allows a werewolf to retain his or her human mind while transformed, thus freeing them from the worry of harming other humans or themselves.

Because werewolves only pose a danger to humans, companionship with animals whilst transformed has been known to make the experience more bearable as the werewolf has no-one to harm and will be less willing to harm him/herself.

According to Gilderoy Lockhart, the Homorphus Charm can force a werewolf back into human shape. But, since Lockhart is known to have lied many times to inflate his own reputation and implies that the charm cures werewolves, his information is highly suspect — as is the very existence of a Homorphus Charm in the first place.

Contrary to what the Muggle world believes, werewolves are not affected by silver.

Prejudice and discrimination
"My kind don't usually breed! It will be like me, I am convinced of it &mdash; how can I forgive myself, when I knowingly risked passing on my own condition to an innocent child? And if, by some miracle, it is not like me, then it will be better off, a hundred times so, without a father of whom it must always be ashamed!"

- Remus Lupin on his fear that he would pass lycanthropy on to his then-unborn child

Werewolves are generally regarded with fear and disgust by wizarding society. It is not uncommon for persons known to be werewolves to be shunned by society and discriminated against within the wizarding world. It is very difficult for a werewolf to get a job in the wizarding community, especially after the passing of restrictive anti-werewolf legislation by the prejudiced Dolores Umbridge in the 1990s. As a result, many werewolves suffer poverty; Remus Lupin managed to get by with the aide of his friend James Potter, and later by working as Defence Against the Dark Arts professor at Hogwarts, though it is unknown how he subsisted between James' death and working as professor. He decided to resign from this position after his condition was exposed as most parents would not want their children being around a werewolf, despite the safety precautions Remus and Albus Dumbledore took.

The Ministry of Magic attempts to regulate werewolves. By 1637, there was a Werewolf Code of Conduct, and according to Newt Scamander, werewolves have been shunted between the Beast and Being divisions of the Department for the Regulation and Control of Magical Creatures for years. At one point, the Werewolf Registry and Werewolf Capture Unit were both in the Beast Division, while at the same time the office for Werewolf Support Services was in the Being Division.

Given Kingsley Shacklebolt's friendship with Remus Lupin and the furthering of Muggle-born and house-elf rights after 1998, it is likely that the reforms of the Ministry under Minister for Magic Shacklebolt included less prejudicial treatment of werewolves.

Retaliation
"He regards it as his mission in life to bite and to conta­minate as many people as possible; he wants to create enough were­wolves to overcome the wizards. Voldemort has promised him prey in return for his services. Greyback specialises in children... Bite them young, he says, and raise them away from their parents, raise them to hate normal wizards. Voldemort has threatened to unleash him upon people's sons and daughters; it is a threat that usually produces good results."

- Remus Lupin on Fenrir Greyback

Due to the oppression and discrimination against werewolves by society, some people who are werewolves have in turn come to hate their oppressors and, in turn, society in general. These werewolves have organised themselves into their own society. Under Fenrir Greyback's leadership, this society works to infect as many people as possible, especially children, with the goal of one day having enough strength to take control of the wizarding community.

The werewolves under Greyback's command served Lord Voldemort in the Second Wizarding War, though Remus Lupin spied on them for the Order of the Phoenix and the Death Eaters looked down on them; for example, they were not permitted to have the Dark Mark. They were used as a threat to ensure ordinary citizens' compliance with Voldemort; for example, five-year-old Montgomery was fatally attacked by Greyback after his mother refused to cooperate with the Death Eaters. Although only Greyback is explicitly mentioned as participating, werewolves under Greyback's command may have fought alongside the Death Eaters in the Battle of Hogwarts. They were most likely sentenced to Azkaban for life for uniting with Lord Voldemort, or killed for resisting arrest.

Known werewolves

 * Fenrir Greyback — a leader in the werewolf community and an ally of the Death Eaters, noted to be the most savage werewolf in history, incarcerated or killed after the Second Wizarding War.
 * Remus Lupin — bitten by Fenrir Greyback as a child, member of the Order of the Phoenix, killed by Antonin Dolohov.
 * The Wagga Wagga Werewolf — discussed by Gilderoy Lockhart during his time as Defence Against the Dark Arts professor at Hogwarts; also discussed in his book Wandering with Werewolves. Lockhart may have invented this individual entirely, but since he often simply took credit for others' deeds, the werewolf itself may have existed, but been defeated by someone else.
 * An unidentified werewolf on Arthur Weasley's ward during his stay at St Mungo's Hospital for Magical Maladies and Injuries, this new werewolf was presumably befriended by Lupin.
 * A group of werewolves living underground, most of whom joined forces with Voldemort for a better life.

Other victims of lycanthropy

 * Bill Weasley — attacked by Fenrir Greyback while he was in human form; Bill did not actually become a werewolf, although he did obtain some "wolfish tendencies" (particularly a liking for rare steaks).
 * Other victims at The Battle of Hogwarts - it could be assumed that there were more victims at The Battle of Hogwarts that suffered from lycanthrophy to some degree in later days like Lavender Brown (it is unclear whether she was actually bitten). It would be similar to the effects suffered by Bill Weasley at the hands of Fenrir Greyback. Although Greyback is described in his animalistic form during the battle and bitting people that were down (The Elder Wand Chapter), it is assumed that he was in human form as Remus Lupin was also in the Battle in human form.

Behind the scenes

 * Professor Quirinus Quirrell had the first year Defence Against the Dark Arts class copy notes about how to treat werewolf bites. Also, Professor Severus Snape assigned an essay during the 1993-1994 school year when he substituted for Lupin, although werewolves were not due to be covered until the last chapter of the third-year DADA textbook.
 * Gilderoy Lockhart claimed he once cured a werewolf of its affliction, although this was almost certainly untrue.
 * According to Draco Malfoy and Argus Filch, there are werewolves in the Forbidden Forest, though it is unclear if these are rumours or the truth.
 * Tom Riddle once accused Rubeus Hagrid of raising "werewolf cubs" under his bed as a youngster, though this was possibly a lie or an exaggeration. It is unknown whether werewolves have cubs or not — Remus Lupin was worried that it might be possible to pass his affliction on his son, but Newton Scamander suggests otherwise. Since Riddle was trying to frame Hagrid, the veracity of his statement is questionable.
 * Lord Voldemort referred to werewolf offspring as cubs another time. When at the Malfoy Manor, he ridicules the Malfoys and Bellatrix about the marriage of Remus Lupin and Nymphadora Tonks, asking Draco if he will "babysit the cubs." Given his purist attitude and disdain for 'half-breeds' this is far more likely to be a derogatory insult rather than an implication that lycanthropy is inheritable.
 * In the Harry Potter and the Prisoner of Azkaban novel, the werewolf form is noted to be only vaguely distinguishable from a true wolf. In the film adaptation however, Lupin's werewolf form is still roughly human-shaped, though gruesomely stretched. His fur is a minimal coat rather than shaggy and he alternates between standing on his legs and scrambling on all fours. J.K. Rowling also noted that to her, "werewolf" means An American Werewolf In London, whose werewolf is an extremely animalistic wolf-shaped beast, but that she was very pleased with the Azkaban film's imagining of the concept and appreciated the sympathy evoked by the "naked" and "pathetic" aspects of the design.
 * In the book it says that when Lupin drinks the potion he just sits in his study until everything is over, however, in the movie Harry Potter and the Prisoner of Azkaban Lupin does not transform until he sees the Moon. Which in some circumstances will be impossible in the castle. As the Moon was rising over a mountain at the time, though, it is likely that this would be the time of night when his transformation begins anyway, and actually being there at moonrise was a coincedence.
 * According to W.O.M.B.A.T., it is possible that werewolves may have a shorter snout than a true wolf. It is rumored that if a werewolf mates at the full moon it will produce a wolf cub instead of a human baby, but given prejudice, lies and half-truths against werewolves, this is most likely not true.
 * In an interview, J.K. Rowling has stated that lycanthropy is a metaphor for HIV.
 * There are two known werewolves, Fenrir Greyback and Remus Lupin. Bill Weasley was bitten by Greyback in a human form, so he will only have a few symptoms of lycanthropy, and not be a full werewolf.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * 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 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 Half-Blood Prince (video game)
 * Lego Harry Potter: Years 1-4
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1
 * Harry Potter and the Deathly Hallows: Part 2
 * Fantastic Beasts and Where to Find Them