After Mary Jane Kelly's murder, there is a scene where Abberline hands Gull a photo of her body. That photo is an actual crime scene photo of the real Mary Jane Kelly.
For dramatic effect, the scene where Richard Mansfield changes on-stage shows him transitioning from Jekyll to (the more monstrous) Hyde. In reality, Mansfield's transformation was the opposite, from Hyde to Jekyll (more consistent with the depicted scene in Robert Louis Stevenson's novel), and involved standing beneath theatre lights, which made him sweat enough for his make-up to run off his face. A simple, but effective, illusion that, by all accounts, still startled the late-Victorian audience.
Sir Michael Caine was persuaded to return to television for the first time in nearly twenty years because of David Wickes's powerful script. Caine later described Wickes as "the nicest, fastest director I've worked for, and the master of filming Victorian London."
In real life, George Lusk was a mild mannered, community-spirited man who sought to assist the police in catching the murderer.