This time we are very well acquainted with the Eleventh Doctor. He’s our pal and the companion will be the new person. So I wanted somebody with a bit more mystery to them, someone you have to get to know in a way that you didn’t have to get to know Amy because we met Amy and the Eleventh Doctor at that same time. Someone more challenging and difficult, someone who will lead him in a merry dance. I always felt that Amy and the Eleventh Doctor grew up together. They’re like childhood friends. It’s a very different feeling now. Steven Moffat Talks Doctor Who, Sherlock — Vulture