Knockers were elves believed to work in Cornwall's mines. Celts generally saw elves as living in families. Because the Cornish excluded women from mines, the same restriction applied to their underground spirits, which appeared as diminutive bearded men, forever digging in abandoned drifts.

Originally, knockers rewarded virtue by revealing valuable ore and by warning of danger when they knocked on timbers before a collapse. The Industrial Revolution ended the practice of Cornish miners working claims for their own profit. Corporate owners paid wages to workers, reducing the role of knockers to that of merely cautioning miners.

When the Cornish came to the American West, they brought their beliefs. Other miners, regarding the immigrants as experts, adopted many Cornish practices and folklore. Contrasting with Cornwall's traditions, the American Tommyknocker was often more ghostly, but this supernatural miner still warned of danger.

Nevada references to Tommyknockers occurred throughout the nineteenth century. Most take the form of hauntings, but occasionally the Tommyknockers's elf-like nature shines through. Belief in Tommyknockers apparently survived longer in Nevada than in their homeland. Interviews with miners as late as the 1930s suggest the western tradition persisted while it was largely extinct in Cornwall by 1900.