Werewolf

A werewolf is a human being who, upon the full moon, involuntarily transforms into a dangerous, wolf-like creature. This condition, known as lycanthropy, is an incurable magical affliction most often transmitted when a werewolf in their transformed state bites a human. During their transformation, werewolves lose their human mind and memory, becoming a threat to any person they encounter, including friends and family. This has led to them being feared and heavily stigmatized within the wizarding world.

• Human Form: In their human form, werewolves are indistinguishable from other people for most of the month. However, as the full moon approaches, they may take on a sickly or pale appearance. Remus Lupin, for example, was often described as looking weary and ill, with his shabby clothing reflecting his difficulty in maintaining steady employment due to his condition.
• Wolf Form: The transformation at the full moon is painful and non-negotiable. The resulting creature appears very similar to a true wolf, though with subtle, non-wolfish characteristics. Remus Lupin's form was described as having a gaunt, wolfish face and a lupine body, but it was clear to Sirius Black and James Potter that it was not a true wolf. In this state, the werewolf has no conscious control and is driven by an instinct to hunt and attack humans above all other prey. They do not retain their human intelligence, making them a separate entity from an Animagus, who transforms at will and keeps their mind.
• Lycanthropy Transmission: The curse of lycanthropy is blood-borne and transmitted through a bite where the werewolf's saliva mingles with the victim's blood. Not every attack results in transmission. Fenrir Greyback, a notoriously savage werewolf, made it his mission to bite and contaminate as many people as possible, particularly children, in order to build an army to challenge the wizarding world. He was responsible for infecting Remus Lupin as a young boy.

While lycanthropy is incurable, its effects can be managed.

• Wolfsbane Potion: A complex and costly potion invented by Damocles Belby. If taken daily in the week preceding the full moon, it allows the werewolf to retain their human mind after transforming. The drinker becomes a harmless, sleepy wolf who will curl up and await the moon's waning, posing no threat to others. Severus Snape brewed this potion for Remus Lupin during his time as a professor at Hogwarts School of Witchcraft and Wizardry.
• Containment: Before the invention of the Wolfsbane Potion, and for those who could not afford it, the only solution was secure confinement during the transformation. At Hogwarts, Albus Dumbledore had the Whomping Willow planted over a secret passage leading to the Shrieking Shack in Hogsmeade, providing a safe, isolated place for Remus Lupin to transform during his school years.

Werewolves are one of the most ostracized groups in the wizarding world. They are subject to immense fear, prejudice, and discriminatory laws enacted by the Ministry of Magic.

• Legislation: The Ministry maintains a Werewolf Register and enforces a Werewolf Code of Conduct. Many werewolves avoid signing the register, fearing the associated stigma. During her time at the Ministry, Dolores Umbridge was responsible for passing new anti-werewolf legislation that made it nearly impossible for werewolves to find employment.
• Social Outcasts: Due to this prejudice, most werewolves live in poverty on the fringes of society. This isolation made them a key target for recruitment by Lord Voldemort, who promised them greater rights and acceptance in exchange for their allegiance. Fenrir Greyback became the leader of the werewolves who sided with the Death Eaters.

• Remus Lupin: A member of the Order of the Phoenix and a close friend of James Potter, Sirius Black, and Harry Potter.
• Fenrir Greyback: A savage werewolf and Death Eater who embraced his condition and sought to create more of his kind.
• An unnamed wizard who was a patient in the “Dai” Llewellyn Ward for Irremediable Charm Damage at St. Mungo's Hospital for Magical Maladies and Injuries, believed to have been bitten by a werewolf.

• J.K. Rowling has stated that lycanthropy was intended as a metaphor for blood-borne illnesses that carry a heavy stigma, such as HIV and AIDS, and the irrational fear and prejudice they can provoke (J.K. Rowling interview).
• In the film adaptation of Harry Potter and the Prisoner of Azkaban, Remus Lupin's werewolf form is depicted as a tall, emaciated, and unnervingly humanoid creature rather than a traditional wolf, emphasizing its nature as a corrupted human form (film).
• On Pottermore, Rowling revealed that werewolf pups do not exist; the condition is only transmittable by a bite. If two werewolves were to mate in their wolf forms (an unlikely event, as they lose their human affections), they would produce normal wolf cubs (Pottermore).