What ARE Dementors?

[sbursztynski]

No: HPFGUIDX 94159

I've wondered for a long time ... exactly what ARE the Dementors? I
mean - we know what they DO, but that's it. And they are sentient -
they make
alliances and somehow communicate with (Ministry) wizards. Are they
born like
that? (The mind boggles at the thought of Dementors with mates and
children! :-D) Are they former humans, like vampires, who have died
and come 
back in some nasty form? Maybe victims of their Kiss come back as 
Dementors? In any case, I haven't spotted any evidence for what they
are, in 
canon, but perhaps someone else has?

Sue B