I don't know who it is but I sure as hell know his real name is not John Harrison. That's the phoniest name I've ever heard. It's a gotta be an alias.
John Harrison was the name of the British clockmaker who invented the marine chronometer and thereby enabled ships at sea to calculate their longitude for the first time. He was one of the most important people in the history of transportation.
It's also the name of quite a few other people
, including a diplomat, a filmmaker, a few politicians, a couple of athletes, a folk musician, a stamp engraver, etc.
Oh, and the Internet Movie Database has 44 John Harrisons
who are real people, but surprisingly, only one to date who's a fictional character, not counting Cumberbatch's role.
Hmm... John Harrison... Jonathan Harris... English accent... oh my gods, he's Dr. Smith! He's seeking revenge for the pain, the pain.