What pair of authors used themes and characters from a fairy tale published in 1812?
Snow White "Snow White" is a 19th-century German fairy tale which is today known widely across the Western world. The Brothers Grimm published it in 1812 in the first edition of their collection "Grimms' Fairy Tales". It was titled in German: Sneewittchen (in modern orthography "Schneewittchen") and numbered as Tale 53. The name "Sneewittchen" was Low German and in the first version it was translated with "Schneeweißchen". The Grimms completed their final revision of the story in 1854.
Childe Rowland "Childe Rowland" is a fairy tale, the most popular version written by Joseph Jacobs in his "English Fairy Tales", published in 1890. It was based on a Scottish ballad, which is why the text alternates between prose and rhyming stanzas. Joseph Jacobs called the King of Elfland's palace "the Dark Tower" in his version, an addition he made that was not part of the original ballad. This harks to Shakespeare's "King Lear" and Robert Browning's poem "Childe Roland to the Dark Tower Came," but neither of those references have any relation to the fairy tale.