Dementors are the darkest creatures in our world. They feed off of despair and hopelessness by sucking up all the happiness in the air. The area around them gets colder "By ten degrees", and they can even put out any light source nearby them.

They are invisible to muggles, but they have the same effect on them as they do on wizards. They gaurd Azkaban, the wizard prison.

Besides their ability to suck happiness, they can give whats call the "Dementor's Kiss", which will extract the soul from the victim.

Dementors are similar to the lethifold.