In think Stefan wrote Ripper because he had an interesting idea for a historical fiction book on Jack the Ripper. No, he didn't have a son, but this idea of Carver, an orphan trying to track his criminal father, made a great book. The story also includes the New Pinkertons, a secret organization that act as the law enforcement with their own rules. Their leader, officer Tudd, would serve as a side antagonist towards Carver because he would use Jack's own son to catch the infamous killer and bring fame to the New Pinkertons for doing what the normal police couldn't. Overall, Stefan used Jack the Ripper's fame to create a fictional story that would be unique and different than other historical fiction books.
I think the most important character in Ripper is Carver. Besides Carver being the main character, he's the one trying to find his father and catch a criminal at the same time. He's experiencing a lot of betrayal from Tudd who's using him for the same goals he has, and from a couple of New Pinkerton agents who were friendly until Tudd gave the order to keep Carver as a prisoner. Carver is also being taught by Hawking and using the gadgets of the New Pinkertons, he might catch Jack. Doing this will get Carver the answers he's always wanted and enough respect to join the New Pinkertons for real or regular law enforcement.