Why do Kobolds care about Cobalt?

A long time ago, in a silver mine far, far away, some post-Roman pre-Euro Germans got tricked.  They pulled out some precious ore and went to go smelt it.  But wait!  Some mischevious spirit had replaced their precious silver ore with something as dangerous as it was worthless.  Upon trying to smelt it, poison seeped into the air and hurt the poor miners.

They decided these spirits must be the mysterious Kobolds - stories had told of small green creatures that lived in the rocks just as humans lived in the air.  Knowing that these Kobolds were themselves masters of mining and metalworking, the miners appealed to their good natures to respect their fellow miners and share the copper and silver.

Sadly the Kobolds didn't listen, and they kept stealing all the precious metals and trying to kill the miners with imitation silver.  Except sometimes they warned the miners away from dangerous areas with loud knocking.  Very polite of them.

Then came the magical 18th century, and whilst the French and American people were busy trying to kill their rightful rulers, some wacky Viking in a lab coat finally pointed out that this crappy ore was in fact metal, and a good one at that - eventually it was used to make super strong alloys and radioactive medicine.

Image courtesy Greg Robson, and of course the guy in the lab coat

It got named Cobalt in thanks to those woefully misunderstood spirits of the earth, who all along were trying to give the miners a precious gift.