A Fae with the ability to change aspect, appearance, and temperament

Dear Great Internet Brain,

Is there a type of fairy/fae that changes according to human belief, or an old story of this happening? What I'm looking for is similar to have Brownies and Boggarts are related (Brownies are beneficial or at least neutral, Boggarts are malevolent, but one can turn into the other depending on how they're treated), but in a larger sense. I'm looking for a type of fae that morphs based on the preconceptions of the humans living in their area (tall/short, handsome/grotesque, beneficial/malevolent, etc). I mean the Brownie/Boggart thing might work, but I was trying to find out if there were other instances of that type of relationship. American Indian, European/English or even Russian traditions would work here. Also, any references you could point to would be fabulous.