Frankenstein: Who is the monster?

I just saw an encore screening of the National Theatre's 2011 production of Frankenstein, with Benedict Cumberbatch as the creature and Jonny Lee Miller as Victor. Even though it was on film, I was completely mesmerized. The physical stamina Cumberbatch possesses is extraordinary - but his inner emotional presence is beyond. I wish I could have seen the two men switch roles, as they did each night during the production. It would be interesting to see Miller as the creature and Cumberbatch as Victor. Perhaps one day I will get the chance.