Wikipedia
The name "Wiedergänger" refers to different zombie or ghost phenomena from different cultural areas. The word means "one who walks again" in German, the etymology relates to Germanic wieder "with, more apart, against, contrary to, re-" (* ̯ui-t[e]ro-, meaning more apart, farther away. diverged, gone apart. nowadays weiter does not only denote a greater distance but also the continuation of an action. ) and gänger, "foot, walker", and the core of the wiedergänger myth is the concept of the deceased, who—often in the form of a physical phenomenon—return (as " undead") to the world of the living (cf. French revenant, "one who is returning"). They usually cause problems and frighten living people. They exist either to avenge some injustice they experienced while alive, or because their soul is not ready to be released, as a consequence of their former way of life.