The role portrayed by Bill Nighy was initially given to Alan Rickman, but the latter had to pull out of the project due to ill-health, which eventually led to his untimely death from pancreatic cancer in January 2016. At the end of the end credits, the following dedication appears on the screen: "This film is dedicated to the memory of Alan Rickman".
Though the film is based on a work of fiction, three of the readers in the library, all of them suspects in the golem case, are real people who did at the time live in London: Karl Marx, George Gissing and Dan Leno.
Though only appearing in the movie briefly, philosopher Karl Marx was indeed living in London at the time the movie is set. Because he was both a Jew and propounded socialist ideas, he was actually harassed by the police and considered -although very briefly- as a person of interest in the Jack the Ripper case.
Director Juan Carlos Medina hired the cinematographer Simon Dennis and the production designer Grant Montgomery because he was very impressed by their work on Peaky Blinders (2013).
William Blake's "The Ghost of a Flea" appears both as the design on the backdrop of Dan Leno's stage show, and as a picture in the Library book.