The Elf King king is a ballad written by the German poet, Goethe, in 1782. Put to music by Schubert in 1815. It tells the sad tale of a father riding home with his son in his arms (presumably the boy is ill). The boy sees feverish images of the Elven king, imagery of death, who tries to lure him to the 'other side'. The boy frantically cries out to his father for help. The Elven king is relentless and threatens to take the boy by force. When the father reaches his destination the boy has passed away.
Constant also made an etch of the Erlkönig.
The numbering is for practical reasons to distinguish between different works with the same title.