What fantastical/fairy tale creatures are associated with 'doing the work behind the scenes'?

In some fairy tales little dwarfs/elfs/pixies/??? perform some work on behalf of the protagonist. Santa Claus has his elf helpers who, at least in some cultures, manufacture the toys. Is there a joke/humorous phrase in everyday english about a task being done by those creatures, used when wishing to either abstract away or keep the person(s) responsible secret? If so, is the mental association strong enough that even their name only brings this particular context to mind?
Not my case, but, for example, hanging out a sign/note ‘pixies(?)’ on the doors in an office as an allusion to doing the real work without receiving recognition?

This is certainly a cultural thing, but considering that fairy tales are pretty much shared between all but all european countries without much variation, I suspect that such an idiom/association exists.