The Black Bull of Norroway was first recorded by Joseph Jacobs, a famous folklorist, literary critic and historian, in his book More English Fairy Tales. In the Aarne-Thompson Tale Type Index. The Black Bull of Norroway is an Aarne-Thompson type 425A, a search for a missing husband. The tale is claimed by a number of cultures, including Celtic and Scottish.
The use of the word “Norroway” may point to the fact that many of the people who settled in Scotland were also from Scandinavia—Norway. However, the content of the story is typical of Scottish, not Scandinavian, folktales.
J.R.R Tolkein, author of The Lord of the Rings, cited the ending of The Black Bull of Norroway as an example of a eucasthrophe in his essay On Fairy-Stories. Tolkein coined the word himself to mean a sudden turn of events at the end of a story which ensure that the protagonist does not meet some terrible, impending and very plausible doom.