Hobgoblin is a term typically applied in folktales to describe a friendly but troublesome creature of the Seelie court.
The most commonly known Hobgoblin is the character Puck in Shakespeare's A Midsummer Night's Dream. Puck, however, is only another name given to a much older character named Robin Goodfellow. However, the origins of his name can be controversial.
Hobgoblins seem to be small, hairy little men who—like their close relative, Brownies—are often found within human dwellings, doing odd jobs around the house while the family is lost in sleep. Such chores are typically small deeds, like dusting and ironing. Oftentimes, the only compensation necessary in return for these was food. Attempts to give them clothing would often banish them forever, though whether they take offense to such gifts or are simply too proud to work in new threads differs from teller to teller.
While Brownies are more peaceful creatures, Hobgoblins are more fond of practical jokes. They also seem to be able to shape-shift, as seen in one of Puck's monologues in A Midsummer Night's Dream. Robin Goodfellow is perhaps the most mischievous and most infamous of all his kind, but many are less antagonizing. However, like all of the fey folk, hobgoblins are easily annoyed. When teased or misused excessively, Brownies become Boggarts—creatures whose sole existence is to play tricks and cause trouble for people. They can be mischievous, frightening, and even dangerous, and they are very difficult to get rid of.
The term "hobgoblin" has grown to mean a superficial object that is a source of (often imagined) fear or trouble. Probably the most well-known example of this usage is Ralph Waldo Emerson's line, "A foolish consistency is the hobgoblin of little minds," from the essay Self-Reliance.