Elf

An elf (plural: elves) is a type of supernatural being in Germanic mythology and folklore. Early elves, whose description depends almost entirely on Norse mythology texts, were a race of beings with magical skills, ambivalent towards humans and capable of either helping or hindering them. But Christianized societies were viewing elves in increasingly sinister light. In Anglo-Saxon England as early as the 10th century, Old English medical books attest to elves afflicting humans and livestock by "elf-shots". The German elf or alp was seen as an "addler" of people in medical books, but already in the High Middle Ages there were prayers warding against it as the agent causing nightmares, and eventually for the alp its identity as nightmare spirits became predominant.

In English literature of the Elizabethan era, "elves" became conflated with the "fairies" of Romance culture, so that the two terms began to be used interchangeably. Romanticist writers were influenced by this (particularly Shakespearean) notion of the "elf," and reimported the word Elf in that context into the German language.

A number of ballads in the British Isles and Scandinavia, perhaps stemming from the medieval period, describe human encounters with the elf, elven-king, elf-maid, etc. The same ballad type (cognate ballads) are often disseminated over several countries. Some common motifs, which may also be seen in British and Scandinavian folklore, are elves enticing men with their dance, and causing death, either by elf-shot or entirely unexplained. In Scandinavia, the elf are often conflated with the beings called the huldra or huldufólk.

Source: http://en.wikipedia.org/wiki/Elf