The Klabautermann is a goblin, but by no means one of the mischievous ones. On the contrary: the popular belief surrounding the Klabautermann is actually really scary.
Since the first half of the 19th century, the story has been told of a goblin who haunts ships and knocks on the ship's walls. He wants to show that the wood from which the ship's walls are made is defective. The knock then meant either: Repair your ship, or: It's all too late and your ship will sink.
The word itself comes from Low German and probably belongs to the verb “kalfatern” – the nautical term for “to seal”.
