The undead are beings in mythology, legend, or fiction that are deceased but behave as if alive. A common example of an undead being is a corpse re-animated by supernatural forces by the application of the deceased's own life force or that of another being (such as a demon). The undead may be incorporeal like ghosts, or corporeal like vampires and zombies. The undead are featured in the belief systems of most cultures, and appear in many works of fantasy and horror fiction.