Various kind of demons appear in Sluggy Freelance. They come in an almost unlimited variety of sizes and shapes, but practically all are intelligent supernatural beings malevolently disposed towards humanity. Demons inhabit more than one demonic alternate dimension of their own, and most that have been seen in the "regular" dimension of Sluggy have been summoned there from somewhere else.
Different types and classifications of demons that have appreared in the comic include:
- Demons of the Dimension of Pain
- Demon Lords
- The Demon King(s)
- Possession demons
- Soul-dealing demons
- The rayths would resent being called demons, but they are so similar the difference comes down to nit-picking.
Some demons can't be classified beyond their individual identity; at least K'Z'K is unique, as the demon predicted to bring about the end of the world (or, as some say, who is literally The End), though he has also acted as a possession demon.