"Dobby is a house-elf"

Elves are magical creatures, originally found in German mythology.  They can be benevolent or malicious (sometimes called "light" and "dark"), and have various magical powers.

The Elves and the Shoemaker by the Brothers Grimm

In The Lord of the Rings, J.R.R. Tolkien conjures an entire race of elves who rule nobly and support the hobbits in their quest.

J.K. Rowling has subverted this tradition, by turning elves into domestic slaves: "house-elves".