Erlking (from Elf-king or Herla-king; German: Erlkönig) is a name from Danish and German folklore for the figure of a spirit or "king of the fairies". While early stories feature the Erlking's daughter as a malevolent figure, Goethe's poem "Der Erlkönig" and those following it have the Erlking himself prey on small children.
According to Jacob Grimm, the term originates with a Scandinavian (Danish) word, ellekonge "king of the elves", or for a female spirit elverkongens datter "the elven king's daughter", who is responsible for ensnaring human beings to satisfy her desire, jealousy or lust for revenge. The New Oxford American Dictionary follows this explanation, describing the Erlking as "a bearded giant or goblin who lures little children to the land of death", mistranslated as Erlkönig in the late 18th century from ellerkonge.
Alternatively, the term may derive not from "elf-king" but from the name of Herla king, a figure in medieval English folklore, adapted as Herlequin, Hellequin in medieval French, in origin the leader of the Wild Hunt, in French known as maisnie Hellequin "household of Hellequin" (and as such ultimately identical with Woden), but re-cast as a generic "devil" in the course of the Middle Ages (and incidentally, in the 16th century also the origin of the Harlequin character). Sometimes also associated is the character of Herrequin, a 9th-century count of Boulogne of proverbial wickedness.
The derivation from either eller- or herla- has not been resolved. Alternative suggestions have also been made, Halling (1836) suggested a connection with a Turkic and Mongolian god of death or psychopomp, known as Erlik Chan.
English Herla is cast in the role of a king of the Britons who ends up spending three centuries in the realm of the elves (and thus missing the Anglo-Saxon invasion of Britain in Walter Map's De nugis curialium (12th century).