Dementor

"Dementors are among the foulest creatures that walk this earth. They infest the darkest, filthiest places, they glory in decay and despair, they drain peace, hope, and happiness out of the air around them... Get too near a Dementor and every good feeling, every happy memory will be sucked out of you. If it can, the Dementor will feed on you long enough to reduce you to something like itself...soulless and evil. You will be left with nothing but the worst experiences of your life."

- Remus Lupin to Harry Potter

A Dementor was a Dark creature, considered one of the foulest that inhabit the world. Dementors fed off human happiness, and thus caused depression and despair to any who were near them. They could also consume a person's soul, leaving their victims in a permanent, and thus were often referred to as soul-sucking fiends. The Ministry of Magic employed Dementors as the guardians of Azkaban until mid-1996, when Lord Voldemort was sighted in the Ministry, and their defection to his side was realised. The Dementors supposedly led the Death Eaters and Voldemort into the Ministry of Magic. After the end of the Second Wizarding War in 1998, the Ministry was reformed, and Minister for Magic Kingsley Shacklebolt ensured that they were not used by the government again.

Dementors held no loyalty, except to whomever would provide them with the most people to feed off. They could not be destroyed, though their numbers could be limited if the conditions in which they multiply were reduced.

Appearance
Dementors had a humanoid shape, approximately three metres, or 10 feet high, and were covered in dark hooded cloaks and ripped, long cloth. The creatures had grey, decayed-looking bodies and their faces had nothing but a large hole where the mouth should have been, which was used for sucking the soul out of the victim in a process called the Dementor's Kiss, which was generally considered worse than death. Unlike other creatures, who move through some means of physical support, Dementors could fly freely.

Nature
"They sort of freeze your insides, don't they?"

- Fred Weasley on proximity to Dementors.

Dementors were at least somewhat sentient, and intelligent enough to be greedy: they obeyed the Ministry of Magic for years because, in guarding Azkaban, they were provided with sustenance. They could understand and follow at least simple instructions, which allowed a Dementor to act as a bodyguard to Minister for Magic Cornelius Fudge in 1995, and for them to escort prisoners in and out of the Muggle-Born Registration Commission courtroom in 1997. They could communicate what they had heard Sirius Black saying in his sleep in 1993 to the Ministry, possibly meaning that they could relay thoughts of their own, or could write, or use sign language of some sort. The extent to which wizards and Dementors could communicate with each other is unclear. It is possible that Dementors reacted to emotion and/or thought, rather than to spoken words, but they could probably hear and understand speech. They were described as having no eyes.

Dementors were said to grow like fungi in the darkest dankest places, creating a dense chilly fog. It was said to be impossible to destroy a Dementor, but their numbers could be limited by eradicating the conditions that allowed them to multiply, implying that they died off eventually. .

Abilities
"They don't need walls and water to keep the prisoners in, not when they're trapped inside their own heads, incapable of a single cheerful thought. Most go mad within weeks."

- Remus Lupin on Azkaban prisoners' long-term exposure to Dementors

Being blind, Dementors sensed and fed on the positive emotions of human beings in order to survive, forcing their victims to relive their worst memories over and over again. The very presence of a Dementor made the victim's surrounding atmosphere grow cold and dark, as the number of Dementors increased so did the effects. Those that were kept in the company of a Dementor for too long became depressed, and were often driven insane, which was the main source of Azkaban's well-deserved horrible reputation.

Although Muggles could not see Dementors, they were affected in a way similar to wizards and witches, becoming depressed when near them. While at least one Squib, Arabella Figg, had claimed to see a Dementor, the truth was that Squibs could not see them, but had enough magical knowledge to identify their effects.

Dementor's Kiss
"There's no chance at all of recovery. You'll just... exist. As an empty shell. And your soul is gone forever…lost."

- Remus Lupin on the Dementor's Kiss

In addition to feeding on positive emotions, Dementors could perform what was known as the Dementor's Kiss, in which a Dementor latched its mouth onto a victim's and sucked out the person's soul. The victim was left as an empty shell, incapable of thought and with no possibility of recovery. It was believed existing after a Dementor's Kiss was worse than death: as a person's soul is their self, to be "kissed" by a Dementor is to cease to exist, and yet also remain. The Ministry of Magic occasionally allowed this as a punishment, before Kingsley Shacklebolt became Minister.

Muggles who had their souls sucked out in a Dementor's attack would mistakenly be thought to suffer from the medical condition known as by Muggle doctors, since after the 'kiss', the victim would no longer experience any brain activity, although no damage had been done to the brain. This makes Dementors even more terrifying, since they would attack wizards and Muggles alike. It is unknown what effect a Dementor's Kiss had on a person who had split his or her soul through use of a Horcrux.

The only recorded Kiss occurred in 1995; Barty Crouch Jr., who had been working in secret for Voldemort, was restrained at Hogwarts for a trial. His soul was sucked out by a Dementor accompanying Cornelius Fudge. A side effect of this act was that it rendered Crouch unable to testify about his master's return, allowing Voldemort almost a full year to gather strength while the Ministry continued in its denial.

After Bartemius Crouch Jr.'s mother died in Azkaban, Dementors buried her body. That shows that Dementors are capable of navvying-type work such as grave-digging.

Protection from Dementors
"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."

- Remus Lupin teaching Harry Potter the Patronus

No one had ever demonstrated the ability to kill a Dementor, implying that they could not be killed through physical means; though they can be driven back. One of the few ways to shield oneself from Dementors was to use the difficult Patronus Charm to drive them away. The charm summoned a Patronus: the magical manifestation of good will and happiness, providing varied levels of protection against the Dementors' influence, based on the caster's strength as a wizard. Only when summoned by an experienced caster would the Patronus take the form of an animal significant in some way to the individual. While the lower level Patronus was more amorphous and ephemeral, corporeal Patronuses would chase down Dementors and force them to flee the vicinity. An incorporeal Patronus could only slow a Dementor down, as if the creature was walking through quicksand, and tended not to last long.

Chocolate was an effective first-aid to mild cases of contact with Dementors. Also, Dementors could not properly sense the thoughts and emotions of a person when he or she took on an Animagus form, which allowed some, such as Sirius Black, to temporarily avoid their insidious influence.

There may be another way of repelling a Dementor besides the Patronus Charm, as Harry Potter disagreed with Professor Snape on the best method for confronting one when it was the subject of a report in his sixth year. This implied that there were other methods, which seemed further likely given that most Dark Wizards were apparently unable (or unwilling) to produce a Patronus.

Separation from the Ministry
The Dementors served the Ministry of Magic as the guards of Azkaban, because it allowed them to feed on the emotions of the prisoners. However, by July 1996, most of the Dementors of Azkaban staged a mass revolt against their employers to join Lord Voldemort, who offered them more victims. This aided the 1996 and 1997 escapes of Death Eaters from Azkaban.

By mid-1996, the Dementors, who had joined Voldemort, were multiplying, thus causing an "unseasonal" July mist. Cornelius Fudge also admitted they were factors in the British Prime Minister's recent decline in terms of public approval, as they were making people less happy in general.

When Kingsley Shacklebolt became Minister for Magic after the end of the Second Wizarding War in 1998, Dementors were no longer used by the Ministry of Magic, presumably because they were deemed untrustworthy and inhumane.

Harry Potter's encounters with Dementors
"When they get near me -- I can hear Voldemort murdering my mum."

- Harry Potter on the Dementors' effect on him

1993-1994
Harry Potter first encountered Dementors during the 1993–1994 school year, when they were sent to guard Hogwarts School of Witchcraft and Wizardry against Sirius Black, who had recently escaped from Azkaban. Harry, whenever he got near one, was forced to relive his worst memory: hearing the last moments of his parents' lives before they were murdered by Lord Voldemort. The first of these encounters was on the Hogwarts Express, during which he was protected by the new Defence Against the Dark Arts professor, Remus Lupin. While the Dementors were at Hogwarts, Headmaster Albus Dumbledore warned the students not to give the Dementors any reason to harm them.

Harry endured a second encounter with a group of Dementors during a Quidditch match, which caused him to lose consciousness and suffer a fall from his broom. He was that time rescued by Dumbledore, who slowed Harry's fall and then drove the Dementors away with a Patronus. They seemed to be particularly attracted to Harry because, due to his miserable childhood and many bad memories, he was particularly vulnerable to their influence.

To overcome the Dementors, Harry asked Professor Lupin for assistance. Lupin taught Harry the Patronus Charm. Harry's Patronus took the form of a stag, just like that of his father. Harry initially failed to produce a fully formed Patronus when he and Sirius were attacked by a group of Dementors in the Forbidden Forest. The two were saved by the intervention of a powerful and fully formed Patronus, which had in fact been conjured by Harry, who travelled back in time with Hermione Granger by use of her Time-Turner. (This technically counts as both Harry's third and fourth encounters with the Dementors, since, due to his time traveling, he experienced this same encounter twice.) Because the Dementors tried to use the Dementor's Kiss on Harry during this encounter in the Forest, it was enough to convince the Minister for Magic Cornelius Fudge to have the Dementors removed from Hogwarts at the end of the school year.

1995
Harry's fifth encounter was in an alley near his home on Privet Drive, when he and his cousin Dudley Dursley were ambushed by two Dementors, sent secretly and illegally by Dolores Umbridge. He was able to successfully use the Patronus Charm and was subsequently rescued by a Squib named Arabella Figg. Harry was put on trial for his use of underage magic, but ultimately not punished, as it was in self-defence.

1997
While Harry was disguised as Albert Runcorn he encounters the dementors in the Muggle-Born Registration Commission court room where the dementors were used to take away witches and wizards who were tested to see if they were of pure blood statues.

1998
During the Battle of Hogwarts, the Dementors fought on the side of Lord Voldemort and the Death Eaters. Harry, Hermione Granger, and Ron Weasley were attacked by large numbers of them, and due to the horrific events they had experienced and witnessed, including the recent death of Fred Weasley, they all had difficulty summoning their Patronuses. Seamus Finnigan, Luna Lovegood, and Ernie Macmillan drove them off with the charm.

Etymology

 * The name Dementors likely comes from the words dement, "to make insane", and tormentor, "one who afflicts with great suffering", which would make the definition of the word "one who inflicts insanity".

Behind the scenes

 * J. K. Rowling has revealed that the inspiration for Dementors came from her bout with severe depression prior to her phenomenal success. She described as an "absence of being able to envisage that you will ever be cheerful again. The absence of hope. That very deadened feeling, which is so very different from feeling sad."
 * In an attempt to sabotage Harry during a Quidditch match in 1993, Draco Malfoy, Vincent Crabbe, Gregory Goyle, and Marcus Flint dressed up as dementors to scare him. Malfoy was standing on Goyle's shoulders. Considering how tall dementors are (they are described in Prisoner of Azkaban as reaching from the floor to the ceiling on the Hogwarts Express), the foursome appear to account for two dementors, when just a few pages earlier, Harry saw three dementors. However, their attempt failed when Harry cast a Patronus Charm at them. As punishment Professor McGonagall gave them all detention and deducted 50 points from Slytherin, plus a serious discussion with Headmaster Albus Dumbledore.
 * Animatronic dementors appear in Harry Potter and the Forbidden Journey at The Wizarding World of Harry Potter, chasing the riders' flying bench through the Chamber of Secrets and around the skeleton of the Basilisk. The Dark Mark appears along with them, suggesting that a Death Eater summoned them to Hogwarts.
 * According to W.O.M.B.A.T., Dementors may be unknown in tropical regions.
 * In Lego Harry Potter: Years 1-4, a large Dementor serves as the final boss of Year 3.
 * J.K. Rowling has said that Dementors breed like fungi.

Foreign words for Dementor include:
 * Chinese 摄魂怪 = "devil strange"
 * Finnish "ankeuttaja", from "ankeus" = "drearyness"
 * French "détraqueur" = "that which makes (things) go wrong or break down"
 * Hebrew "סוהרסן", from "סוהר" = "prison"
 * Japanese 吸魂鬼 = "intake/suction soul demon"
 * Vietnamese "giám ngục Azkaban" = "director of Azkaban"
 * Czech "mozkomor" = "plague of the soul"
 * Indonesian "iblis" = "demon of death and happiness remover"

Appearances

 * 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 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
 * Harry Potter and the Deathly Hallows: Part 1
 * Harry Potter and the Deathly Hallows: Part 2
 * Harry Potter and the Deathly Hallows: Part 1 (video game)
 * Harry Potter and the Forbidden Journey

Notes and references
Détraqueur Dementor Дементор סוהרסן Ankeuttaja