Demons are not native to the world of Gloriana. They enter the world through magical gates to spread chaos and desolation upon everything. The gates are opened by means of negative energy released through death or destruction. Such gates are usually temporary unless sustained by a "Gate Orb" -- a magical device that draws magic and negative energy from the air in order to maintain a gate. The largest of these gates are known as a World Gate.
There are many types of Demons. Some are mindless creatures of destruction, some are merely stupid, and some are very intelligent, capable of using magic. All Demons thrive upon killing living things. Demons are resistant to fire and damage from non-magical weapons. They may be highly intelligent and magic-using (Demon Wizards), or just stupid and tough (Dumb Demons), but all Demons are dangerous.
Demons crave the taste of blood, the scent of fear, and the power that killing releases.