Demons are born in the Under-Realm. Like in Aravorn, demons have various species - some more simple-minded than the rest. Their purpose is to shepherd the living into death. They are beacons of death and crave it - but death is not a bad thing to them. They could even be likened to angels, since eternity in bliss or in agony is up to the individual to decide.
However, the Demons the people of Aravorn tend to have the most successful relations with are relatively human in form.
They can be distinguished by a pair of vestigial wings, and tail. Demons are never truly unarmed, for even without a weapon their fingers double as claws.
Though possessing wings, demons are incapable of flight unless using magic or some other means. However, their wings definitely aid in balance.
Demons also possess perfect night-vision, which means the more nefarious of their kind tend to prefer to do their activities under the cover of night.
Demons can summon other demons, but it's unwise unless they have the power to control them
Demons tend to be rather impulsive, meaning they take chances another being may avoid. They are however an intelligent race, capable of thought just like humans and elves.
As for most people, the aims govern a big part of their behaviour. Also their acquaintances have a big influence on them. For demons this results in wildly different lifestyles: Demons who only know other demons and undead tend to attack humans or elves on sight, not knowing any better. However, populations of demons who have lived together with mortal races tend to integrate quite well: They want to be accepted. Only a small streak of mischievousness remains to set their behaviour apart.
Demons and Magic
Demons are a very magical race, though a good portion of their powers tend to have chaotic manifestations, which doesn't do much to improve the image of the race as a whole.
 Prominent Demons
Loren the Amazon Princess