The knocker is one of the many kinds of Cornish faery. It is an ugly creature with a hooked nose that stands no more than three feet tall and lives underground in the Cornish tin mines. They are known as knockers because of the knocking sound they made with their picks and shovels as they too mined the tin. A wise Cornish miner would set aside a small portion of his meal to win the favour of the local knockers as it was well known that the knockers knew where the richest veins of tin were located, and would make them known to those whom they favoured.

Some say that they are the spirits of old miners, others that they are the souls of the Jews who crucified Christ condemned to spend the rest of eternity in limbo. Which is why, it is said that on certain days of the year such as Christmas Day and Easter Day they can be heard singing carols in the mines as their penance.