Virtually every film in modern memory ends with some variation of the same disclaimer: "This is a work of fiction. Any similarity to actual persons, living or dead, or actual events, is purely coincidental." The cut-and-paste legal rider must be the most boring thing in every movie that features it. Who knew its origins were so lurid? For that bit of boilerplate, we can indirectly thank none other than Grigori Rasputin, the famously hard-to-assassinate Russian mystic and intimate of the last, doomed Romanovs. It all started when an exiled Russian prince sued MGM in 1933 over the studio's Rasputin biopic,...