Taylor Lautner has been called a "rare breed" for taking it upon himself to bulk up for 'New Moon'.
The 17-year-old actor stars as werewolf Jacob Black in 'The Twilight Saga' but almost lost the role in the second movie - which was a bigger part than he had played in the first - until he piled on the muscle to turn himself into a "leading man".
Screenwriter Melissa Rosenberg - who has worked on all the movies - told Film.com: "Taylor is unusual because he easily could have lost that part. He was a day player in the first movie, and there were all these discussions about whether he'd be coming back.
"He took it upon himself to transform himself into a leading man. He made himself a leading man. That was nobody but him, he made that for himself.
"Taylor Lautner is a rare breed. He wanted something and he made it happen. It easily could have gone the other way, if he doesn't do anything maybe it doesn't happen for him. Incredibly driven. That character is such a physical character that it had to be a transformation."
Meanwhile, Taylor's co-star in the franchise, Robert Pattinson - who plays vampire Edward Cullen - is also said to be bulking up for his role in the final instalment of the series, 'Breaking Dawn'.
The 23-year-old British star is reportedly on a high-protein diet and has amazed diners at his local Nando's chicken restaurant by popping in regularly for meaty treats.
A source said: "He is a regular visitor to the Victoria branch in London. The customers can never believe it is really him - or how much he eats. He's mad about the peri peri chicken."
'Breaking Dawn' - which may be split into two separate films - is due for release in 2011.