Imps are often described as mischievous more than seriously threatening, and as lesser beings rather than more important supernatural beings. The attendants of the devil are sometimes described as imps. They are usually described as lively and having small stature.
The Old English noun impa meant a young shoot or scion of a plant or tree, and later came to mean the scion of a noble house, or a child in general. Starting in the 16th century, it was often used in expressions like "imps of serpents", "imp of hell", "imp of the devil", and so on; and by the 17th century, it came to mean a small demon, a familiar of a witch. The Old English noun and associated verb impian appear to come from an unattested Late Latin term *emputa (impotus is attested in the Salic law), the neuter plural of Greek ? 'natural, implanted, grafted'.
Originating from Germanic folklore the imp was a small lesser demon. Unlike the Christian faith and stories, demons in Germanic legends were not necessarily always evil. Imps were often mischievous rather than evil or harmful and in some regions they were attendants of the gods.
A legend in Lincolnshire dating to the 14th-century recounts that the devil, being annoyed with the completion of the cathedral, paid a visit, accompanied by two imps who proceeded to wreak havoc in the building. An angel appeared and ordered them to stop. One turned to throw a rock at the angel and was instantly petrified.
For the tiniest angel, with amethyst eyes,
And hair spun like gold, 'fore the alter [sic] did rise,
Pronouncing these words in a dignified tone
"O impious imp, be ye turned to stone!"
While his companion fled, the unfortunate imp remains at the Angel Choir at the east end of the cathedral.
The Legend of the Imp King dates back to 12th-century Scotland, and talks about how the Devil stole a child and replaced it with an imp in the cradle. The imp grew up with a hateful grudge against the Devil, and eventually returned to hell where he started a revolution. He called upon all of the other imps and hell-hounds and all other minor beasts to join his fight for revenge. Calling himself the Imp king, he grew a crown of horns and led the largest army of demi-demons into the throne room of hell, where he was ultimately victorious as the other side surrendered and volunteered to be his slaves for life. A mission began to retrieve his stolen siblings and give them pleasant lives in his newly conquered lands; finally being awoken from their long, long slumbers.
Imps are often shown as small in stature and not very attractive. Their behaviour is described as being wild and uncontrollable, much the same as fairies', and in some cultures they are considered the same beings, both sharing the same sense free spirit and enjoyment of all things fun. It was later in history that people began to associate fairies as being good and imps as being malicious and evil. However, both creatures were fond of pranks and misleading people. Most of the time, the pranks were harmless fun, but some could be upsetting and harmful, such as the switching babies or leading travelers astray in places they were not familiar with. Although imps are often thought of as being immortal, they can be damaged or harmed by certain weapons and enchants, or be kept out of people's homes by wards.
Imps were also portrayed as lonely little creatures in search of human attention, using jokes and pranks to attract human friendship. This often backfired when people became annoyed with the imp's endeavours, usually driving it away.
Even if the imp was successful in getting the friendship it sought, it still often played pranks on its friend either out of boredom or simply because this was the nature of the imp. This trait led to using the word "impish" for someone who loves pranks and practical jokes. Eventually, it came to be believed that imps were the familiar spirit servants of witches and warlocks, where the little demons served as spies and informants. During the time of the witch hunts, supernatural creatures such as imps were sought out as proof of witchcraft, though often the so-called imp was merely a black cat, lizard, toad or some other form of uncommon pet.
Imps have also been described as being "bound" or contained in some sort of object such as a sword or crystal ball. In other cases imps were simply kept in a certain object and summoned only when their masters had need of them. Some even had the ability to grant their owner's wishes much like a genie. This was the object of the 1891 story The Bottle Imp by Robert Louis Stevenson, which told of an imp contained in a bottle that would grant the owner their every wish, but their soul would be sent to Hell if they didn't sell the bottle to a new owner before their death.
Imps can be found in art and architecture throughout the world, most of the time carefully and painstakingly hidden and only being found by the most interested and observant of people.
In Final Fantasy Legend II, the imp is one of the three selectable monsters at the beginning of the game.
The dictionary definition of imp at Wiktionary