G+: Elf on the Shelf
Originally started out as a promotional item with chocolate at Christmas, I think, and then people (like my mom) started collecting them. They came in different size and different colored elf suits, and the first I remember them was in the mid to late Sixties. The "Elf on the Shelf" picture book came later, after people started family traditions to use their collections of elves to mess with their kids' heads.