Viggo Mortensen doesn't talk with his hands so much as he batters the air. When he's making a point about the human need for compassion, he snatches two handfuls into his chest. When he's discussing fear, he tomahawks the table. If something served as a wakeup call for the actor, he slaps his face. Hard.

"It's OK to be intense," Mortensen says. "Especially if the movie calls for it."

And few movies call for intensity like Mortensen's new film, The Road, which opened in limited release the day before Thanksgiving. It has been well received by critics, including USA TODAY's Claudia Puig, who called Mortensen's performance "superb, blending a weathered demeanor with indefatigable determination and tenderness."

The movie, based on Cormac McCarthy's Pulitzer-prize winning book, is a grim tale about a father (Mortensen) and son (newcomer Kodi Smit-McPhee) trekking through a post-apocalyptic landscape in search of food, shelter and humanity.

He and Smit-McPhee spent months shooting in the damp winter woods of Pennsylvania, wearing little more than rags. Though Mortensen won't say how much weight he lost in preparation for the nameless role, he is clearly emaciated in one scene of The Road.

"He's a passionate guy," says The Road director John Hillcoat. "If you don't have an actor who will commit to this kind of material - and a lot of actors won't - the movie falls apart. Because he's in virtually every single frame. It's all on his and Kodi's shoulders."

That he would be the anchor for Hollywood films is a byproduct of intensity that Mortensen didn't expect. Born in New York to an American mother and Danish father, Mortensen, 51, spent years in Argentina, Denmark and Venezuela for poetry and photography. "I know it sounds clichéd, but I didn't want to do anything for fame," he says. "I just love the arts."

And while he landed parts in big films such as Carlito's Way, Crimson Tide and G.I. Jane, it wasn't until Mortensen received a phone call from New Zealand that his fate changed.

Peter Jackson says he had noticed Mortensen in a handful of small roles and knew of the actor's commitment. "I just didn't know how gung-ho he'd be for everything," says Jackson, who cast Mortensen as Aragorn in the Lord of the Rings trilogy.

If a scene called for Mortensen to climb a mountain face, "he'd be the guy who slept outside in a sleeping bag to get a start on the day," Jackson says.

Mortensen's on-screen persona can conflict with his demeanor in person, says Fran Walsh, Jackson's partner and Lord of the Rings co-writer.

"He is so kind and playful and funny off set," Walsh says. "He's almost like a hippie. We picked him up at the airport one time, and he wasn't wearing shoes. I still have no idea how he got through the airport barefoot."

That tender side was on call for much of The Road shoot, which made friends of Mortensen, the father of a grown son, and Smit-McPhee, now 13. "They would take breaks from the shoot, and Viggo would show Kodi all of the sword moves he learned for Lord of the Rings," Hillcoat says. "They became true friends."

One scene, in particular, bonded the two, Mortensen says. The script called for Smit-McPhee to be bathed in the cold water of a wash basin.

"It really was cold, and Kodi began to cry," Mortensen says. "John was going to stop shooting and Kodi used it. Did it all in one take. He's as committed an actor as anyone I've worked with."

That's a growing list. After Lord of the Rings made him an A-list actor, Mortensen starred in David Cronenberg's A History of Violence and followed that up with the lead in 2007's Eastern Promises, which earned him a best-actor Oscar nomination.

The actor calls the film "the ultimate love story. What do you do when you lose everything? When you're stripped bare? There's love. There's kindness."

Mortensen raises his arms and locks his hands behind his head.

"I don't think that's corny," he says. "I guess I'm old-fashioned, but I like movies that are committed to telling a story that might be brutal but isn't afraid to show unabashed kindness. That's a commitment I try to have."