Benedict Cumberbatch says he's one of the ''stupidest actors'' around.

The 42-year-old screen star is preparing for his upcoming role as real life British spy Greville Wynne in Cold War movie 'Ironbark' and he has previously played WikiLeaks founder Julian Assange in 2004 movie 'The Fifth Estate' and the star has revealed he likes to play the role of ''smart characters because he is drawn to them'' because they are so different to who he is.

Speaking to Stellar magazine, Cumberbatch said: ''The great joy [of acting] is the transformation - moving away from what I know or who I am. So perversely, I am probably one of the stupidest actors I know. I'm playing some of the smartest characters because I'm drawn to them. They are so different from me.''

Cumberbatch is best known for portraying geniuses on-screen as he has also portrayed mathematical expert Alan Turing in 'The Imitation Game' and the brilliant, albeit fictional detective, Sherlock Holmes in the TV series 'Sherlock' written by Steven Moffat and Mark Gatiss.

His latest movie sees him voice the titular and cunning character 'The Grinch' in the upcoming animation based on the 1957 Dr. Seuss book 'How the Grinch Stole Christmas!', and he admitted found working alone on the project presented new challenges to him.

He told The Hollywood Reporter: ''It was weird. It was wonderful. It was everything that being a voice artist is on a long-haul project like this. It was a lot of fun. Hard work but fun.''

Cameron Seely, 11, voices the character of Cindy Lou Who and although she and Cumberbatch's Grinch have most of their scenes together, they never met during recording.

Benedict said: ''It's an odd thing to not be in the room as her, but that's not a novelty for anyone who's ever done one of these [animated films] before. It's bizarre to meet Cameron for the first time during promotion for the movie.''