John Blair, professor of medieval history at Oxford University, discusses a 12th-century text known as The Life and Miracles of Saint Modwenna, which is one of several medieval manuscripts recounting events that took place nearly a thousand years ago. These folktales tell ghastly stories of the walking dead.
The walking undead in medieval texts do quite a lot of different sorts of bad things. Some of them come back and attack their own relatives and friends, some of them spread disease, some of them do suck blood just like Dracula. Some of them just spread fear.