The haugbui or Aptrgangr is a fierce monster from Norse mythology.
Haugbui means howe or barrow, a reference to the grave. Aptrgangr means after goer, a reference to something that walks after its dead.
The haugbui was created when a freshly deceased corpse was possessed by a demonic entity. It was said to be able to inflate in size and to exhibit huge strengh, in a similar way to the demons in the Evil Dead movies
The Aptrgangr is similar to the Draugr except that it prefers to remain in his grave whereas the Draugr frequently raided entire villages.