The film is based on the life of Manuel Blanco Romasanta, a Galician peddler who lived in the first half of the 19th century and was the author of thirteen crimes, also considered the first and only case of lycanthropy in Spain.
Juan Antonio Porto, the film's screenwriter, was also the great-great-grandson of Romasanta's defense attorney.
Final film of María Fernanda Ladrón de Guevara.