Mark Ruffalo, the most likable guy in Hollywood, is hitting his stride in upstate New York.
Credit: Aby Baker / Getty Images

So there's this little kid named Nicholas. Five years old, lives in New York City, goes to elementary school down in the Village where the parents get to hang out with the kids for a half-hour every morning, just talking or coloring or whatever. A nice, safe place.

One morning, Nicholas is there working at his little table, when his classmate Odette comes in and sits down with her dad. Nicholas thinks Odette's dad looks familiar, but he's not sure from where. He looks at him for a minute. Goes back to coloring. Looks again. Colors some more. Looks one more time. Finally, he can't help himself.

"Are you the Hulk?" Nicholas asks.

Odette's dad laughs. "Well," he says, "not really...."

"Yes he is," Odette says. "He's the Hulk."

"I'm not really the Hulk," the dad insists. "I just play the Hulk. I do it in the movies."

"Yes you are," says Odette. "You're the Hulk!"

Odette's dad gives up. "OK, I'm the Hulk."

Nicholas, satisfied, goes back to coloring. But now his little mind is whirring, an idea taking shape. After a while, he looks up again.

"Turn into the Hulk," Nicholas says.

Odette's dad laughs again. "You want me to turn into the Hulk?"

"Yeah."

He shrugs, like, if you say so. "OK...."

At this point in his story, Mark Ruffalo – sitting down for breakfast a few blocks from the school – starts cracking up. "So I look at him," Ruffalo says, "and I go like this." He flares his nostrils, bulges out his eyes, and starts to shake, uncorking that fist-clenching fury that means mild-mannered Bruce Banner is about to become the Incredible Hulk. Nicholas starts to scream, "No, no, no, not in here! You'll break it, you'll break it!" Ruffalo just laughs.

On the face of it, this story is a little tough to believe. Just look at this guy – typical 45-year-old Manhattan dad in a gray sweater, jeans, and black running shoes, with a few days' worth of graying beard, a big, goofy smile, and that prairie-flat Wisconsin accent, carrying a white bike helmet decorated with stickers of kittens and puppies. Who could possibly mistake this guy for a gamma-irradiated rage monster? But Ruffalo's capacity for transformation can be startling. Just ask Nicholas. Or 'Avengers' co-star Scarlett Johansson.

"Mark and I shared our first day on 'Avengers' together," says Johansson, "and in between each take he looked at me panicked and kept saying, 'Maybe they can recast me, it's not too late!' He was fumbling with his lines and nervous and unsure of himself. Everyone thought he had really dropped the ball. Little did I know he was crafting total brilliance. When I saw the final cut, I told him what a sneak he was – and of course all he did was smile mischievously."

Ruffalo's breakfast comes – soft-boiled eggs, coffee, toast – and he slides the kitten-and-puppy helmet out of the way to make room. The helmet belongs to Odette, who catches a ride to school on the back of her dad's bike every day, come rain, snow, or shine. Until recently, he and his wife of 14 years, Sunrise, were living with the kids in a big farmhouse upstate, but they moved back to New York so that their two older kids could go to a school with a strong program for dyslexia. Ruffalo thinks he may have been dyslexic growing up, and he doesn't want his kids to fall behind the way he did.

Ruffalo has three children: five-year-old Odette, eight-year-old Bella Noche, and 11-year-old Keen. None of them had names until well after they were born. "We had a lot of names picked out," Ruffalo says. "But when Keen was born, we took one look at him and said, 'None of those fit.' For the first two weeks we tried a new name every day: Hi, Clyde. Hi, Tony. Hi, Frank. Hi, Romeo. Then after two weeks, we got a phone call from the Department of Records: 'Hey – you haven't picked out a name for your kid! You have until 12 o'clock today, otherwise his name is going down as Baby Boy Ruffalo – and it's really hard to change.'"

Ruffalo happened to have a big Webster's dictionary, and he started flipping through it. When he got to the K's, he called to Sunrise: "Baby? What about Keen?" She asked what it meant, and Ruffalo told her: sharp, interested in, fond of, and also, a low, braying, mournful cry. "She was like, 'That's perfect.'"

Plucking your kid's name out of a dictionary 30 minutes before deadline is a pretty Mark Ruffalo thing to do. He is a dreamer, a drifter, a real liver-in-the-moment. Ever since his major movie debut as Laura Linney's slacker brother in 2000's 'You Can Count on Me,' he's been a go-to guy for charming, soft-spoken characters who don't quite have their shit together – loving-yet-quirky boyfriends, flawed, sensitive cops. It's a testament to Ruffalo's extreme likability that his characters tend to be endearing even while doing some pretty uncool things, like his Oscar-nominated turn in 'The Kids Are All Right,' as a free-spirited sperm donor who nearly torpedoes a 20-year marriage and still comes off like the best dude in the room.

For a long time, Ruffalo was an indie idol – the broody guy with the cuddly good looks you'd see in quiet dramas about broken relationships and poor life choices. Even in big prestige films, like 'Collateral' or 'Zodiac,' he tended to work subtly and at the margins, and in his paycheck rom-coms like 'Just Like Heaven' and '13 Going on 30,' he seemed like he opened the wrong door and stumbled on set from some smaller, better movie. He's even that way when he's playing a superhero: Ruffalo's Hulk – funny, nuanced, sweetly disheveled – is basically an art-house Hulk, the indie-est Hulk imaginable.

Still. Since his Oscar nod and 'The Avengers,' Ruffalo's been getting the kinds of roles that typically go to movie stars. Take his new movie, 'Now You See Me'. It's a mainstream summer bauble with Woody Harrelson and Morgan Freeman, where Ruffalo plays an FBI agent hunting some bank-robbing magicians. Ruffalo is pretty excited about it. "I could be eating my words," he says, "but it looks like fun." It's a departure for him, in that it's a summer popcorn flick with no aspirations to anything greater. He says he took it because it sounded like a blast, which is why he does most things. "I'd never done an action movie," he says. "Halfway through filming, I turned to my wife, and I said, 'Baby, I'm only doing action movies from now on. It's so fun! I don't have to torture myself. I don't have to tie myself up into knots. I just get to run, jump on stuff, and be cool.'"

Over the years, Sunrise Ruffalo has been a sounding board for many of her husband's fantasies. Back in his twenties, Ruffalo used to surf in Baja a lot, and for a while he was this close to spending the rest of his life riding waves and fixing surfboards. When he filmed 2003's 'In the Cut' with Meg Ryan, Ruffalo played an NYPD homicide detective, and he'd spend days drinking with them in bars and smoking cigarettes and hanging around the station house, wishing he was a cop for real. In another movie called 'Windtalkers,' he was a Marine and was ready to enlist. "This is awesome!" he told Sunrise. "They tell you exactly where to go, what to wear, you get three squares a day.... If I work really hard, I think I can make it to captain!" And after the movie he just wrapped called 'Foxcatcher,' the true story of a champion Olympic wrestler who gets murdered by a schizophrenic millionaire, Ruffalo wanted to get back into wrestling – competitively, at age 45. Sunrise's response? "That's awesome, Mark."

This is clearly not a man burdened by anything so oppressive as a master plan. He's more like an eager Labrador, always ready to go in the backyard and play. "He gets 100 percent into everything that he does," says his mom, Marie. "It's never a drag, always an adventure." "He is enthusiastic about everything," says Johansson. "Especially if it's potentially disastrous."