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.
In The Spiderwick Chronicles, Hogsqueal, the anti-hero of the fantasy saga by Holly Black and Tony DiTerlizzi, is a hobgoblin. In these stories a hobgoblin is a mischievous, albeit good natured goblin.
In the English translation of Finn Family Moomintroll, the third book of the Moomin series of children's books by Tove Jansson, the Hobgoblin is a strange magical personage -- even his hat, when found by other creatures, can work strange sorts of magic all by itself. While slightly frightening to those who don't know him, he is in fact a rather lonely and sensitive creature, who can grant the wishes of others but not his own: unless somebody specifically asks him for something which he wants, and then gives him what he himself created.
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. Often, 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 clothes differs from teller to teller. It is possible that the 'hob' in their name comes from the hob, a part of the hearth meant for holding food or utensils.
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 fae 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.
An example of a boggart is in Harry Potter: Prisoner of Azkaban, where the creature lives in a cupboard and takes the form of what people fear.
