There are a couple of theories about the nature and orgin of the dementors. One is that dementors are the byproduct/result of The Dementor's Kiss: once someone is rendered soulless by the Kiss, he/she becomes a dementor. Therefore, they need not reproduce like normal creatures, but the "Kiss" is their method of asexual reproduction, kind of like "siring" a vampire in most vampy fictional universes. There's a snag, though: under this theory, where did the first dementor come from? Maybe it was wizard-bred, but what kind of sick bastard would... oh, wait. Nevermind.
In terms of canon evidence, we know very little about them except what we see them do and what Lupin tells Harry during their tea-time session in
PoA. Dementors are not mentioned in
Fantastic Beasts and Where to Find Them, which in general only discusses those magical which fall under the "Beast" division, not "Being" (house-elves, for example) or "Spirit" (like ghosts). I'd wager they count as Spirits, since I can't see them participating in wizarding government.
That said, it'd be really awful if, as some theorists predict, those who go through the veiled archway in the Department of Mysteries become dementors. There are worse things than death, indeed...
After writing the above, I came across an article I do not remember reading, in which Jo herself addresses the issue.
Source: Canadian Press article by Dene Moore, "Harry Potter author fields questions from junior journalists in Vancouver," 25 October 2000, archived
www.quick-quote-quill.org/articles/2000/1000-canadianpress-moore.htm.Erm... a fungus, eh? *is too tired to ponder such a thing* Moving on.
Anyhow ... seeing as the Dementors were only employed by the Ministry after the initial 'fall' of Voldemort, did it used to just be guarded by regular wizard-folk with baton-wands and tazer-charms?
The answer depends on how gut-wrenchingly stupid you think the Ministry was the first time around. During the rebirthing party, Voldemort names the dementors as part of his to-be-
recalled army to Harry and the circle of Death Eaters. Even if he's stretching the truth like he usually does, it implies that they worked for him the last time around. But we know that at least as of Karkaroff's hearing in the
GoF Pensieve, which took place after Voldemort's "fall," the dementors were working for the Ministry as prison guards and courtroom bailiffs.
However, in
OotP Petunia seemed to know that the dementors guarded Azkaban. If
she is telling the truth about having heard such things from "that awful boy" James, then the dementors were guarding Azkaban
well before Voldemort became Vapormort at the hands of baby Harry. After all, we're told in Boolk 1 that Petunia and her sister, and presumably her sister's husband James, hadn't met in quite some time.
So had the dementors worked for Voldemort, wreaking havoc for the Dark Lord, then switched sides? The brief exchange between Moody and Dumbledore on the subject during Karkaroff's hearing might suggests that the dementors' employment by the Ministry was a controversial issue. Funny how Dumbledore can forgive and trust
Snape but not the dementors...
I can well imagine that dementors would have no real loyalty, but what would induce them to pull such a Snape-like switcheroo? Maybe it's too much work for them to seek out their prey, and they would rather feed on corralled souls in prison. Or maybe Voldemort treated them badly. Would he be immune to them, since he doesn't seem to have any happy thoughts? The Death Eaters are probably a rather cheerless lot, too -- though if Azkaban has imprisoned Death Eaters, the prison isn't exactly a dementor smorgasboard, either. Maybe dementors would really prefer to be carneys, where they'd be surrounded by happy, laughing people all the time....
Or perhaps this is just a problem of continuity. Jo appears to have invented the dementors relatively late in the game, certainly after she had finished the early chapters of Book 1. Jo claims to have named them in 1998, as she mentions in the "Harry Potter & Me"/A&E "Biography" segment in which she displays the paper trail of notes, drafts, and sketches she generated in creating Harry's world.
Source: "Harry Potter and Me"
(BBC Christmas Special, British version), 28 December 2001, transcribed by Marvelous Marvolo and Jimmi Thøgersen for Madam Scoop's Index,
www.mutabilisdesign.com/harry/hp01-bbc.htm.And as a related FYI... One of the rejected alternatives to
Dementor was
Excubitor, which is Latin for "sentry," as I explain here:
www.hpana.com/forums/topic_view.cfm?tid=11771
