Yes! TanRu and Mumblethrax Googled my mind. From
http://en.wikipedia.org/wiki/Erlking:
The Erlking (German: Erlkönig, "Alder King") is depicted in a number of German poems and ballads as a malevolent creature who haunts forests and carries off travellers to their deaths. The name is an 18th-century mistranslation of the original Danish word elverkonge[citation needed], "elf-king". The character is most famous as the antagonist in Goethe's poem Der Erlkönig and Schubert's musical adaptation of the same name.
But "Erle" was also a surname in Dunsany's family. His brother was Admiral The Hon. Sir Reginald Aylmer Ranfurly Plunkett-Ernle-Erle-Drax, KCB, DSO, JP, DL.
We also have the name of the hero, Alveric, which means "ruler of elves" in Old Norse. So we have a curiously circular setup: The Elfking asks his son, the King of Elves, to go marry the King of Elfland's daughter. Is Dunsany making a joke or foreshadowing something in the story? Or is he really lazy when it comes to making up names, like a lot of otherwise good GMs?