Demons are a race of magical beings motivated by Evil. They seek out to kill innocents and the forces of Good. Demons are unable to feel emotions and possess no soul or conscience. Almost all demons are immortal, and in some occasions, however, a demon can become good and desire to live a mortal life.
For centuries they have been ruled by The Source of All Evil, who claimed to be the most powerful of all demons. Most demons live in the Underworld or the mortal world, depending on what goal they wish to achieve or how they influence the mortal world. When exiled, a demon is not allowed to live in or enter The Underworld which is punishable by death.
Demons are said to come in every shape and form. And while that is true, most demons seem to have a human appearance, either by nature or with magical help. It is also possible for demon to have an amorphous body instead of physical form.