Who wrote the poem described here, which is perhaps most best known as a song composed by Franz Schubert?
"An anxious young boy is being carried at night by his father on horseback... As the poem unfolds, the son claims to see and hear the "Erlkönig" (Elf King). His father claims to not see or hear the creature, and he attempts to comfort his son, asserting natural explanations for what the child sees – a wisp of fog, rustling leaves, shimmering willows. The Elf King attempts to lure the child into joining him, promising amusement, rich clothes and attentions of his daughters. Finally the Elf King declares that he will take the child by force. The boy shrieks that he has been attacked... Upon reaching the destination, the child is already dead."
Johann Wolfgang von Goethe