Pullman revealed that he made the decision to join Torchwood before he even finished reading scripts for the first few episodes.
"I hear the voice in the writing. This knows itself. It's a concoction. It's an ambitious motherf**ker," Big Shiny Robot quotes him as saying. "I want to be scary, boring, philosophical, funny, touching. I'm going to risk things. Exploding tension with the possibility that a laugh increases it."
The actor continued: "I didn't even finish reading the first three Torchwood scripts and I didn't even finish the second one. I got it before Christmas and reading I was like, 'This is Christmas for me'. It's like opening a present."
Pullman went on to insist that he doesn't consider Oswald to be one of Torchwood: Miracle Day's villains.
He explained: "It clogs the wheels [to call him evil]. This 'You're the bad guy in this movie' kind of talk is a yolk. His point isn't to be sinister. I think sometimes people are [just] scary."
Pullman recently praised Torchwood creator Russell T Davies for helping him to understand Oswald Danes.
Torchwood: Miracle Day continues Thursday at 9pm on BBC One, and airs this Friday at 9/8c on Starz in the US.
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Watch Bill Pullman discuss Torchwood: Miracle Day with Digital Spy below: