Steven Moffat: "Andrew Scott became a star - which he absolutely deserves to be - on the basis of being in the last three or four minutes of Sherlock.
His screen-time was tiny but it’s a measure of that man’s extraordinary talent that he’s become such a big deal so quickly. He’s a genius."source

Mark Gatiss: "What Andrew does astonishingly in this series is the suggestion of bone-deep weariness with existence.
There’s a sort of black— those black eyes— which you can’t quite fathom. It’s really quite chilling.
It’s almost like there’s something else inside him looking out."