You’ve played a lot of intriguing characters over the years–everyone from Alan Turing to the voice of a dragon in The Hobbit to Stephen Hawking. How many of them would you say are geniuses?
I’m not going to do this in any particular order, but Hawking, Frankenstein, Joseph Hooker [the British botanist in Creation], Oppenheimer, Turing, Assange. Van Gogh–a genius. And Sherlock.
I think you also have to count the genetically engineered superman.
Yeah, Khan [from Star Trek] is definitely smart.
You research these men before you play them. Do they have anything in common?
Well, they’re unique personalities–people who are seemingly so different that they remain in existence sort of separate from the rest of us. That is always very attractive to focus in on as an actor. My great enjoyment with these characters is to show that no, they are human beings. They have loves and likes and dislikes. They have all the sort of polarities that we experience in the human condition. But with some sort of special filters added in.
Turing was one of history’s great inventors, credited with pioneering the idea of a programmable computer and envisioning the possibility of artificial intelligence. When you tell people about him, do they know who he is?
No, and they’re shocked. Everyone goes, Why didn’t I know about this story? This man’s achievements are extraordinary. Everything that’s been thrown at computers–all of it has only managed to work because of his idea of creating something universal in the first place.
There’s also a spiritual side to his work, right? He raised questions about free will and machine vs. man.
As a philosopher, he was profoundly affected by the idea that if we could achieve artificial intelligence, could artificial intelligence achieve feeling and what we call will itself? Could it evolve a consciousness? Could it become self-aware? Could it make decisions? Could it fall in love?
Turing’s biographer Andrew Hodges said he was “slow to learn that indistinct line that separated initiative from disobedience.” How much of genius do you think is about rebelliousness?
People who push boundaries help us evolve socially, intellectually, culturally–in any field of life, any sphere.
But at a cost to themselves.
Because they’re in opposition to the majority. But those are the revolutionaries, the pioneers. Those are the people who actually help us, as a race, progress.
How do you convey that kind of complexity and intelligence in a character?
With Sherlock, it’s the pyrotechnic of making the connections very quick. That’s a joy to play. It’s really hard work and it’s frustrating as hell, but it’s very rewarding. But to convey intelligence? I don’t know. Maybe I have my mother to thank for that. Just the eyes, I think they are the windows to the soul. And I think they’re also the windows to the mind that’s driving that soul, doesn’t believe in the soul or is computing whether a soul could be made out of … metal and wire and glass. In the case of Alan.
So it’s about a lot more than dialogue.
Oh yeah. These people are all incredibly different personalities, in their bodies as well as in their minds. The unified things we could talk about are pretty obvious. A lot of them come up against obstacles, whether they’re bureaucratic or conservative. They’re pushing against a sort of unrelenting, unforgiving world that doesn’t want anything out of place or muddled with or made different. Sometimes that’s viewed as arrogance. My argument in humanizing these people–through sort of being an actor who empathizes with his characters–is that [that arrogance] is born out of necessity. It’s not something to judge them by.
Were you into computers as a kid? Not necessarily to the extent of Turing or Hawking–just in general.
I was a little bit, but not to any level of expertise. I wrote programs on BBC computers. We had computing lessons where you’d actually write coded commands to create programs to play little games or build up a Christmas tree on a BBC computer. But computers were more interesting to me when you could put a little packet in them and protect the world from nuclear strike on an Atari console or a Commodore 64. [I also liked] the little Nintendo, the handheld Donkey Kong Jr. things. And then I was always into the Sega Game Gear. That was my real interest in computing–having fun with games.
Do you still play games?
I don’t. I don’t have time. You go to bed at night sweating that you haven’t done a good day’s work or that you haven’t read that book. I’d love to, though.
You recently announced your engagement in the U.K. newspaper the Times, as many British noncelebrities do. How come?
I’m slightly old-fashioned. It’s what I would have done if I weren’t famous. That’s the idea. It’s to normalize it. So it was just about me announcing it in a traditional manner–traditional in the sense that lots of people still do that.
Our Best Inventions package in this issue features new technologies that even the geniuses you play probably didn’t imagine–a wearable chip that buzzes to improve your posture, a smart watch that monitors your heartbeat, even edible ice cream wrappers. Which sounds best to you?
Edible ice cream wrappers, tick. Definitely up for that. Not just because you can eat them, but because they’re biodegradable. That’s where technology should go–toward making us be able to sustain our life here on earth.
This appears in the December 01, 2014 issue of TIME.