Jim Parsons has spoken about his surprise at The Big Bang Theory's success and popularity and describes it as "a glorious surprise".

The CBS sitcom has grown to become the highest-rated show on US television since its launch in 2007, and is now broadcast in over 70 countries around the world.

Parsons - who has won several awards and a star on the Hollywood Walk of Fame for playing scientist and social misfit Sheldon Cooper in the sitcom - said that he never expected the show to be such a global hit.

"It's been a glorious surprise, the whole way," he said. "I knew from the beginning that I felt what we were doing was good work, because we shoot in front of a live audience, I knew they were enjoying it.

"But the idea of whether or not that would translate to a wide enough audience to even stay on the air, much less be popular in several foreign countries, where even to this day I go 'why?'. I just don't get it, but I'm so happy about it."

Parsons also compared Sheldon to his latest character, Oh from the DreamWorks movie Home, and that it was refreshing to play someone who is generally nice, and quite different to Sheldon.

"You have no idea, the heaven it was to come from playing someone sort of anti-social, to someone who kind of wants to embrace everyone and wants to be loved," he said.

"It was like a whole new set of muscles you hadn't stretched in a while."