Most of the beings the spirit world don't care much about mortal business. Those who do, generally out of hunger or a need of terrifying them, are what wizards commonly refer to as demons, as a general term.
Harry Dresden states that they know when you've been bad or good, and they make Santa Claus look like an amateur. Demons don't have a soul, don't worry about good and evil or right and wrong, and if they're inclined to eat someone, they will. There are, however, rules of protocol that demons are obliged to follow, such as offering resistance to any mortal who called them and trying to end the life of the wizard that called them.
In the seriesEdit
In Storm Front, a Toad Demon invades Harry Dresden's apartment in the middle of a storm. It follows Harry Dresden and Susan Rodriguez down to the Dresden's lab where Dresden encloses he and Susan inside of his bronze summoning circle. Dresden and Susan transport outside with the aid of a potion—the demon follows. The Shadowman shows up claiming the demon is his. Harry defeats the demon using the power of the storm.
In Grave Peril, using a ritual spell in his lab's copper Circle, Harry Dresden attempts to summon Azorthragal, Harry Dresden ends up summoning instead assuming Azorthragal is it. Dresden binds the Nightmare to him so he can't hurt anyone else forcing it to come after Dresden only.
In Blood Rites, Harry Dresden fights monkey-like guardian demons that looked like "demented purple chimpanzees" and threw fiery goop to rescue a box full of Temple Dog pups for Brother Wang. Dresden dubs one of the demons Kongtron because it was about eight feet tall and was formed when the smaller demons came together in a fashion similar to the children's cartoon giant robot Voltron. Dresden explained to Thomas Raith that is was a Shen—a chinese spirit creature. Ebenezar McCoy makes reference to the scion of demons when talking about Jared Kincaid.