Bones of Metal
The "bones of metal" as Sidrahkir called them, were forged to appear as skeletons but were made of metal and given life by the magic of the Lunari. Their purpose was to guard the cavern beneath the Dark Valley, and especially the sword of the king, from outsiders and anyone who would seek to ransack or steal. They spent most of their time in the cave sailing from end to end but would go to shore if the need arose.
According to their leader, B'L'T, they were confined to the cave until the final prophecy was fulfilled. After King Belgrave completed the prophecies, nothing was ever heard from the skeletons but there were reports of a "ship of the dead" which had begun to ravage the seas. If they did ever resort to piracy, it was only because their primary purpose had ended and they needed something to do.
There are only three named in the stories, but at least five are known to exist and there could be more.