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.