Most ghosts are seemingly passive or even benevolent, appearing to scare people only by accident, never by intent. Ghosts that are violent (also known as poltergeists), however, are in a class by themselves. Stories suggest that some of these malevolent spirits have actually killed people. The most famous cases of violent hauntings have inspired multiple books and movie adaptations. This list looks at some of the most vicious "true" hauntings around the world and throughout history.