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...soul-less and evil. You will be left with nothing but the worst experiences of your life."

- Remus Lupin to Harry Potter

A Dementor is a Dark creature, considered one of the foulest that inhabit the world. Dementors feed off human happiness, and thus cause depression and despair to any who are in close proximity to them. They are also capable of consuming a person's soul, leaving their victims in a permanent vegetative state, and thus are 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 of Magic and their defection to his side was realised. The Dementors supposedly lead the Death Eaters as well as 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 hold no loyalty except to whomever will provide them with the most souls to consume. They cannot be destroyed, though their numbers can be limited if the conditions in which they multiply are reduced.

Appearance
Dementors have a humanoid shape, approximately three metres in height, but covered in dark, hooded cloaks which reveal only grey, decayed hands and faces. They have no eyes, only a large hole where the mouth should be, which is used for sucking the soul out of the victim in a process called the Dementor's Kiss, which is generally considered worse than death. Unlike other creatures, who move through some means of physical support, Dementors can fly freely, without support.

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

- Fred Weasley on proximity to Dementors

Dementors are 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 are also able to understand and follow simple at least 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 were also able to communicate what they had heard Sirius Black saying in his sleep in 1993 to the Ministry, possibly meaning that they can relay thoughts of their own, or can write, or use sign language of some sort. The precise extent to which wizards and Dementors can communicate with each other is unclear. It is possible that Dementors react to emotion and/or thought rather than to actual spoken words themselves, as they are described as not having eyes. Dementors are said to grow like fungi in the darkest, dankest places, creating a dense, chilly fog. They are apparently invincible, as it is impossible to destroy a Dementor, but their numbers can be limited by eradicating the conditions that give rise to them, implying that they die 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 sense and feed on the positive emotions of human beings to survive, forcing them to relive their worst memories. The very presence of a Dementor makes the victim's surrounding atmosphere grow cold and dark, with increasing effects as the number of Dementors rise. Those kept in the company of a Dementor for too long become depressed, and are often driven insane, which is the main source of Azkaban's well-deserved horrible reputation.

Although Muggles cannot see Dementors, they are affected in a way similar to wizards and witches, becoming depressed when in their vicinity. While at least one Squib, Arabella Figg, has claimed to see a Dementor, the truth is that Squibs cannot see them, but have 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 can perform what is known as the Dementor's Kiss, in which a Dementor latches its mouth onto a victim's and sucks out the person's soul. The victim is left as an empty shell, incapable of thought and with no possibility of recovery. It is believed existing after a Dementor's Kiss is 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 allows this as a punishment.

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

The only known 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.

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 Charm

No one has ever demonstrated the ability to kill a dementor, implying that they cannot be killed through physical means; though they can be driven back. One of the few ways to shield oneself from Dementors is to use the difficult Patronus Charm to drive them away. The charm summons 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 will the Patronus take the form of an animal significant in some way to the individual. While the lower level Patronus is more amorphous and ephemeral, corporeal Patronuses will chase down Dementors and force them to flee the vicinity. An incorporeal Patronus can only slow a Dementor down, as if the creature is walking through quicksand, and tends not to last long.

Chocolate is an effective first aid to mild cases of contact with Dementors. Also, Dementors are not able to properly sense the thoughts and emotions of a person when he or she takes on an Animagus form, which has 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 Sixth Year. This implies that there are other methods, which seems further likely given that most Dark Wizards are apparently unable (or unwilling) to produce a Patronus Charm.

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 following 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 school year of 1993-1994, 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 game, 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 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, which 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. The two were saved by the intervention of a powerful and fully formed Patronus, which had in fact been conjured by Harry himself, 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.)

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.

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 defintion 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 Azaban 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.

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
Détraqueur