What popular 1818 novel had the sub-title 'The Modern Prometheus'?

Answer: The popular 1818 novel that had the sub-title "The Modern Prometheus" is Frankenstein.

Explanation: Frankenstein is a novel written by Mary Shelley, an English author; however, it was first published anonymously in 1818. "The Modern Prometheus" used to be the sub-title of this novel, but it is no longer included in most of its modern editions. This sub-title makes reference to the Greek myth of Prometheus, who is conceived as a hero. In the myth, Prometheus rebels against the gods by stealing fire in order to give it to the humans.