Having a famously vegan and green-minded actress in your cast can have positive effects. Just ask Kenneth Branagh (pictured below), who directed the Oscar winner in the new action fantasy "Thor." When it came to being eco-conscious on set, "We tried where we could to be, led by Natalie Portman who resisted the use of plastic bottles," he says. "She was an influence. And in the action sequences in terms of smoke, the energy we used, it was a factor. I think it is woven into what we do. It is an action movie and you're gonna spill some water every now and again, but I think we attended to it and we did the best we could."

The movie, opening May 6, is based on the Marvel superhero comic book series and figures from Norse mythology. The titular hero (Chris Hemsworth, pictured right with Kenneth Branagh), cast out of the realm of Asgard by his father Odin (Anthony Hopkins), lands in modern-day New Mexico (where he meets the scientist played by Portman) and has to find a way to redeem himself and reclaim his god-dom. The 6'3" actor ("Star Trek") worked out with a trainer and did heavy weightlifting for six months and followed a Spartan diet to prepare for the role. "I had to force myself to eat chicken breasts and rice and steak — the most exhausting part of it was the eating. It wasn't the fun stuff, either. It wasn't hamburgers and pizza," says Hemsworth, who read some Norse myths and enough Thor comics "to get a sense of who he was and the world he was from." He'll reprise his Thor role in "The Avengers," appear in the remake of "Red Dawn" and in the thriller "Cabin in the Woods," and may co-star with Kristen Stewart in "Snow White and the Huntsman."

Idris Elba ("The Wire," "Luther") has little dialogue in "Thor" but clad in gleaming armor and sporting glowing yellow contact lenses he is an imposing presence as Asgard's all-seeing gatekeeper Heimdall. The costume was quite heavy, and though the acting challenge was not, he signed on for the chance to work with Branagh in a genre he hadn't done. "In terms of my experiences, it's one of the most fun," says Elba, for whom recycling "is a daily routine, getting rid of waste that we produce at home." Having shot "Thor" in California followed by a "Ghost Rider" sequel in Turkey, London-based Elba says he's away too much "to make a real dedicated push" towards eco-living. "But I'm about to get a new car and I'm thinking about getting an electric. It's smart with gas so expensive."

He'll return to BBC America in a second season of "Luther" in the fall, and has a role in Ridley Scott's sci-fi flick "Prometheus" that he can't divulge anything about. "I'm sworn to secrecy," he says. "But it's a phenomenal part."

Photos courtesy Paramount Pictures

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