The kobold's origins are obscure. Sources equate the domestic kobold with creatures such as the English boggart, hobgoblin and pixy, the Scottish brownie, and the Scandinavian nisse or tomte; while they align the subterranean variety with the Norse dwarf and the Cornish knocker. Irish historian Thomas Keightley argued that the German kobold and the Scandinavian nis predate the Irish fairy and the Scottish brownie and influenced the beliefs in those entities, but American folklorist Richard Mercer Dorson discounted this argument as reflecting Keightley's bias toward Gotho-Germanic ideas over Celtic ones.