Hulder is a term for a domesticated forest spirit that is often in service to an Elf or their family.
Magnus Chase and the Gods of Asgard[]
The Hammer of Thor[]
Magnus meets a Hulder, that is Inge when he and Hearthstone visit Hearth's home to get the Skofnung Stone back from Alderman. Magnus is surprised to find that Inge is a Hulder and has a cow's tail.
Appearance[]
A hulder is easily distinguished from other residents of Alfheim by their tail. So far, the only known Hulder is Inge, the servant of Alderman and his family. She is further described as a young child with rosy cheeks. Hiding their cow tail would be a crime in Alfheim in the charges of impersonating a proper elf. Iron causes them excruciating physical pain.