The Knocker, Knacker, or Tommyknocker is a mythical, subterranean,
gnome-like creature in Cornish and Devon folklore. Its Welsh counterpart is the coblynau. The name “knockers,” pronounced “knackers,” comes from the
knocking on the mine walls that often happens just before
cave-ins. Known for stealing miner's tools they can also be benevolent helping to warn miners of impending collapse.