Dybbuk

The Dybbuk is a malevolent spirit from Jewish folklore comparable to an "unclean" spirit in other religions, although often considered demons there is a difference between an "unclean" spirit and an actual demon: demons are considered fallen angels or spiritual evils whilst "unclean" spirits such as the Dybbuk are considered the restless souls of unhappy humans or animals (similar to the idea of ghosts).

A Dybull was the spirit of a dead sinner who, instead of continuing on to the afterlife, decidedd to hide out by inhabiting the body of a living person, where they would either live quietly or, more frequently, pester and torture the victim.

According to folklore the victim had to have committed some sort of sin in order for the Dybbuk to get inside, thus it could not harm the "righteous" - if one was possessed by a Dybbuk it could be exorcised by a properly trained rabbi.