The Knocker is the Welsh and Cornish equivalent of Irish leprechauns and English and Scottish brownies. About two feet tall and grizzled, but not misshapen, they live beneath the ground. Here they wear tiny versions of standard miner's garb and commit random mischief, such as stealing miner's unattended tools and food. They are named for their knocking against the walls of mines, either to scare miners or warn them of a cave-in.
"Origin: Wales. A mine fairy that hails from Cornwall. It's said that they knock on walls and tell you where good ore veins are. It's also said that if you look for them, they will get angry and attack you."
"Fairies that inhabit the mines of the Cornwall region of England. They appear as little people and live in mine shafts. Knockers perform acts of kindness towards humans, such as showing them where rich ores lie. However, forgetting to thank a knocker will result in a curse, and the knocker will never again show you where the ore lies. Knockers are also said to be the souls of Jews who were condemned to remain on earth for having crucified Jesus Christ."
"A sprite who lives in the mines of Cornwall. They would notify miners of a good ore-bearing seam by knocking. They are generally good sprites, but show their anger to those they dislike. They hate whistling, so miners never whistle inside mines."
"A sprite who lives in the mines of Cornwall. There are tales of benevolent tapping to tell miners of a rich vein of ore or notifying them of an impending cave-in. They are generally viewed as good sprites, but show their anger to those they dislike. They reportedly hate whistling, so miners who do not wish to draw their ire never whistle inside mines."
—Devil Summoner: Soul Hackers Compendium
Knocker is one of the lowest level demons, and along with Pixie will offer a tutorial on demon negotiations at the Algon NS Building.
In the 3DS remake, a variant Knocker is available from Nemechi, one of the first available from the start. He costs 100 D-Souls and uses the artwork from Shin Megami Tensei: Devil Summoner. This Knocker is notable for having access to Lost Word, a spell normally available to certain high level demons.