Gremlins:
English pilots first started talking about them during the Second World War.
During flights, motors and machine guns would suddenly begin to act up for no reason, and sights and other instruments would malfunction. This was difficult to explain, as aircraft were generally thoroughly checked before every flight.
Counterintelligence officers worked themselves to exhaustion searching for Nazi saboteurs. But what Counterintelligence and numerous commissions failed to do, the ordinary pilots achieved — they found the culprits. They turned out to be tiny evil spirits. They nested in the aircraft — in the grooves and under the plating — and played pranks. They were dubbed gremlins. After some time, gremlins appeared in America. But unlike the English gremlins, they settled in other types of machinery as well.
There were those who took them seriously and there were skeptics. Refusing to believe in evil spirits, they mocked them in every way. Walt Disney was among the skeptics, employing a caricatured image of gremlins. From sinister creatures, they were transformed into funny, cute rascals. Laughter killed the belief, and by the end of the war, people stopped talking about them.

Material from Wikipedia:

Gremlin (EnglishGremlin) — a mythical creature]], a malicious prankster, akin to a domovoy.

Apparently, the term first appeared in 1940 among English pilots and aviation technicians during the Battle of Britain. The first publication regarding the gremlin "phenomenon" was a story in the "Royal Air Force Journal" from April 181942.
It is believed that gremlins love to settle in the engines of cars, airplanes, and other machinery. It is because of their antics that machinery fails to start or even breaks down. To appease gremlins, it was customary to use a mixture of beer and machine oil, which was poured into a tin can and placed in close proximity to the technical unit.


But that's just an aside... Just that if you're going to make creatures, then make them... rather than using a caricature...