"Der Erlkönig" is a poem by Johann Wolfgang von Goethe. It depicts the death of a child assailed by a supernatural being, the "Erlkönig"
The poem begins by giving the impression that the child is simply dying from a vague, unspecified ailment and sees death as a figment of his imagination. As it proceeds, the poem takes an ever darker twist, and ends with the child`s death. -Wikipedia (very good article)