The James Bond actor, who plays Mikael Blomkvist in The Girl with the Dragon Tattoo, told STV that he was determined to look "as normal as possible" for the part.
The 43-year-old explained: "I'd just come off the set of Cowboys & Aliens and I was stick thin, and David wanted me to pile on some pounds.
> Daniel Craig 'dieted' for Cowboys & Aliens
"I just wanted to make [the character] as normal as possible. I really like him: he's idealistic, he believes in fighting injustice.
"He's like a dog with a bone over a mystery he wants to solve, but he runs away when he's scared. He's normal, he's human."
Asked whether he would appear in a sequel, Craig added: "We'll see - we'll see if this one's a success first. I'd love to do it if it was."
> Daniel Craig 'wanted Dragon Tattoo character to be normal'
The Girl with the Dragon Tattoo opened in UK cinemas today (Boxing Day).
Watch the full-length trailer of The Girl with the Dragon Tattoo below: