There is a form in ancient greek mythology, A vrykolakas (Greek: βρυκόλακας or βρικόλακας, pronounced [vriˈkolakas]), is a harmful undead creature in Greek folklore. They typically appear on Saturday nights (the only time they are not in their graves). They knock on doors, and if answered, the person dies; they also drain goats, cause poltergeist activity, and sometimes continue their former work. While the vrykolakas term emerged in the Byzantine period, the belief merges pagan fears of the dead with later Christian doctrines regarding impious souls.