At the same time that Benedict Cumberbatch and Martin Freeman were filming the first season of their awesome British TV show Sherlock, they were both auditioning for parts in The Hobbit franchise that Peter Jackson was directing.
It's a perfect pairing—and for Cumberbatch's representation of Samug it's, obviously, all about the voice. And what a voice. In the video above you can see him audition for the role and see the production team hear him and realise HE HAD TO BE SMAUG. And so it was.
Next step was to put him in one of those ping pong mocap suits and let him do his magic. Even without the post-production he's pretty terrifying.
And then here he is in the final film. The videos are excerpts from the extras on the DVD of The Hobbit: The Desolation of Smaug.