The Dementors are magical creatures from the Harry Potter universe; they first appear in the third book of the series, Harry Potter and the Prisoner of Azkaban, as the guards of the wizards' prison.
Their look, powers and the favourite pub they hang out in.
Dementors wear dark, ragged clothes with a hood that completely hides their face; their hands look like those of a drowned man. Their feet and legs are hidden, and they move as if they are sliding rather than walking.
Only wizards can see them; Dementors are invisible to muggles, even if every mortal is affected by them.
Their presence is marked by a feeling of coldness and despair; Dementors feed on positive thoughts, making people feel that they'll never be happy again.
On selected victims they can perform the Kiss of Death, sucking the soul of mortals and turning them into Dementors.
They make excellent prison guards (even if they are blind, and can only "sense" emotions) because their constant presence slowly drives prisoners mad, and the wizards kept under their influence are too desperate to use magic to escape.
In the first five Potter books, only two people managed to get out of Azkaban...
They feature prominently in The Prisoner of Azkaban, appear briefly in The Goblet of Fire (even if it really was a shapeshifter mimicking one of them) and at the beginning of The Order of the Phoenix we see them attacking two boys. Later we learn that their kind
gave up any pretense of working for the forces of Good, and took side with Lord Voldemort.
In case of a Dementor attack, consult the physician.
Dementors can be fought with the complex Patronus spell, that works only if wizards manage to overcome the despair and concentrate on the happiest thought of their lives.
After meeting a Dementor, it's recommended to eat large quantities of chocolate to regain strength.
Eat your heart out, Hollywood.
Dementors are among the best monsters created in recent years to scare the daylights out of readers and moviegoers.
Consider abysmal failures such as the Creeper and the Death of Final Destination - entities that cannot give us even a half decent nightmare - and you'll realize that it's quite hard to invent new monsters, as opposed to the tired rehash of vampires / serial killers / giant squid that
Hollywood seems to love so much.
Yet Mrs. Rowling managed to pull it off - and remember that the Potter books are aimed at young boys, but read by adults too: Dementors must be quite complex to hit the right buttons for readers of all ages.
A small child is scared by darkness and by the monster in the closet, things that can be dispelled by some good magic, and that simply don't work on an adult.
Grown-ups, on the other hand, fear more complex things - loneliness, old age, or the unexpected IRS envelope - that leave a boy almost unaffected.
A child reads about the Dementors and shivers at their physical appearance - Mrs. Rowling, unlike Stephen King, keeps her horrors fully cloaked to let our imagination work against us. The mental powers and the feeling of coldness are merely a nice side effect for children who have known nothing but love in their lives.
On the other hand, the physical description doesn't bother an adult, who can see the zipper on the monster's back. Yet they have experienced the loss of loved ones, several broken hearts and maybe a bout of depression. They remember the moments when they couldn't conjure up a single happy thought; they read the books, nod and think "yes, that's exactly how it was". Mrs. Rowling understand depression; Dementors were created in a very dark period of her life.
Children fight Dementors by swishing a wand, adults by holding on the memories of better times, and by the knowledge that the clouds will pass; children are tickled by the idea that chocolate has magical restorative powers, adults know this for a fact.
A creepy touch is the fact that Dementors are invisible to non-wizards; the next time that you feel sad or hopeless, you'll think that maybe, just maybe, there is a
hooded figure looming upon you...
'scuse me, have I seen you somewhere before...?
As a final note, in the IMDb you can read that the effects team spent six months creating the look for the Dementors in the movie The Prisoner of Azkaban.
To me, it looks that after six months of horsing around and with a deadline fast approaching, the SFX guys simply made a copy/paste job on the Ringwraiths...
I see that somebody softlinked several nodes about language and gender. My first language is Italian, and I painstakingly polish my English writeups so far as spelling, grammar and style are concerned. If you downvoted this node because you feel that I should spend more effort playing gender games, I'd be glad to discuss this topic with you. In Italian.
Update: I've amended the node to make it non-gender-specific after JudyT kindly /msg'd me (as opposed to the anonymous softlinkers). I still think that some people are a bit too trigger happy about this topic.