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."The seeds of Ruffalo's come-what-may life were sown early on. He was born in Kenosha, Wisconsin, the oldest of four kids. His dad was a Baha'i, sort of the hippies of Kenosha, and Ruffalo went to a Montessori preschool where they threw pottery and weaved God's Eyes. His paternal grandfather was the son of Italian immigrants who ran sugar across the Canadian border for bootleggers during Prohibition. After his sugar-running days were over, Frank Ruffalo Sr. started a house-painting business in Kenosha that Ruffalo's dad, Frank Jr., later took over and turned into a big company, with contracts from American Motors and the U.S. Navy. (Ruffalo's mom was a hairdresser, and the other Ruffalo kids – Scott, Nicole, and Tania – all followed in her footsteps.) When Mark was 13, the family moved to Virginia Beach, where he learned to surf, built skate ramps with stolen plywood, lost his virginity on the first hole of a golf course, played bass in a crappy Fugazi-inspired band called Voice of Reason, terrorized tourists on his motorcycle, and frequently found himself running from the cops for much of the above. In high school, he was voted "Most Fun to Be Around."

Ruffalo was a C student who sucked at math but excelled at wrestling. In 11th grade he placed fourth in the city, and his coach told him that he stood a good chance of earning a scholarship. But Ruffalo was burned out, and quit wrestling for drama. "There were a lot of cute, loose girls," he says, "and the ratio was deeply in my favor."

Ruffalo applied to a bunch of colleges he didn't get into. After he graduated high school, his parents moved again, this time to San Diego, and he went with them. Ruffalo hated it; they lived in a seedy beach community full of burnouts and meth, and his dad, who by this time had quit the painting business, was trying to make a go of it as an entrepreneur, peddling a Sodastream-like invention called the Soda Butler – "He was 20 years ahead of his time," Ruffalo says – but ended up broke and bummed. Soon his marriage splintered, and Ruffalo's dad moved back to Wisconsin and back into painting. ("Within six months," Marie Ruffalo says, "we went from normal to bankrupt and eliminated as a family.")

"I always say he was an artist who never found his art form," Ruffalo says of his free-spirited dad.

Luckily, his son found his. Not long after his dad left town, Ruffalo moved to L.A. and started taking classes at the Stella Adler Academy, where his classmates included Benicio Del Toro and Salma Hayek. He started a no-budget theater company with some friends and paid the rent doing landscaping and painting houses. After a while he talked his brother, Scott, into coming to live with him. They shared a $600-a-month apartment with their cousin, who slept in the living room, and a friend, who slept in the kitchen, while the brothers shared a full-size bed in the only bedroom. ("They were like little bear cubs together," his mom says. "They dug a 20-foot koi pond, lily pads and everything – in South Central L.A.!") For a while Ruffalo's brother was on food stamps. "He'd make a fucking giant bowl of tuna pasta, and we'd eat off that all week long," Ruffalo remembers. "The best of times, the worst of times."

There were a lot of worst of times. They lived near MacArthur Park, which was a dangerous place. "It was the height of the crack wars," he says. "We'd go to the park in the morning and there would be bodies strewn out in the grass. Young women, totally strung out, sores all over their face, would knock on our door asking for money or food. It was so heavy." One day his neighbor got stabbed 12 times on Ruffalo's front porch after he tried to stop some kids from breaking into a car. Another time, Ruffalo was tending bar at a local joint when a gangbanger pulled a gun. The off-duty cop working the door drew his gun, too, and shot the guy dead.

Meanwhile, Ruffalo was going on auditions – roughly 800 of them by his count, which led to exactly zero jobs. Despite his convincing facade of chillness, he would get pretty mad. "I was so frustrated, so angry," he says. He swore off acting four or five times, and sometimes, after really bad auditions, he would come home and punch holes in the wall. (RUFFALO SMASH!)

It didn't help that he was now also tending bar at the Chateau Marmont, where he had a front-row seat to the Hollywood high life. "It was all these young stars," he says. "Johnny Depp, Nic Cage. I was grinding it out doing all these plays, and I couldn't get my foot in the door. I don't know if I was trying too hard, but I just wasn't admitted into that club."

By the mid-1990s, Ruffalo was ready to throw in the towel: "I was doing all these plays, I couldn't get anyone to come. I sucked at auditioning. It was a really low point." Meanwhile, Ruffalo Painting, his father's company, had just gotten a big job from Chrysler and was making money hand over fist. And so, washed up at age 24, Ruffalo moved back to Wisconsin to do sandblasting with his dad.

Ruffalo's mom tried to talk him out of it. "I was very angry when Mark even suggested it," she says. "I said, no way. The idea of any of my children going back to join that painting business would have been disastrous, but with Mark it was especially easy – because I knew he was talented."

Ruffalo found himself in an unusual position: He wanted to settle down and take a nice steady job with the family business, and his mom wanted him to go back to South Central L.A. and live on peanut-butter-and-jelly sandwiches and follow his dream. For a while he toiled away, braving the asbestos and the silica flakes. But, in the meantime, he was also going on business meetings with his dad, where he'd watch him gladhand with the businessmen responsible for making bids.

"What I learned was, this whole American bidding-for-jobs thing is a con," Ruffalo says. "Whatever we want to think about American business – work hard, tell the truth, have morality – it's a myth. There's a lot of graft. They're paying off inspectors. Every day, you're asked to compromise your integrity in some way. And I didn't like it."

Ruffalo stuck it out for a while longer, until finally, fed up with the lying, cheating, and backstabbing that constituted the Middle American painting business, he returned to Hollywood, where, he says, people told the truth, and things made sense.We're finished with breakfast now, and Ruffalo suggests we go sit in the park. The problem is, he's got his bike, which he doesn't want to leave. He looks at the child seat mounted on the back, then at me, then back at the seat. "Well..." he says, "you wanna ride?"

After a slightly wobbly start, we're off, the Oscar-nominated actor pedaling hard up the Hudson Street bike lane with a journalist on the back. He dodges an old lady crossing the street with groceries and manages to avoid being sideswiped by a cab. At one point, I accidentally let the child-seat strap dangle in such a way that it gets caught in the spokes, yanking the chain off the derailleur and sending the bike lurching to a stop. "Don't worry about it!" Ruffalo says, hopping off to inspect the shredded strap. "I've got another one at home." He flips the bike over and starts fixing it in the middle of traffic, practically whistling.

Ruffalo has hit his share of speedbumps in life, but you'd never know it from the way he radiates optimism. As we sit on a park bench next to an old man feeding pigeons, he tells about his first big break, after 'You Can Count on Me'. He was filming 'The Last Castle,' starring Robert Redford. "It was big-time," Ruffalo says. "There I was with one of my heroes, Robert Redford, doing this walk-and-talk. I'm like, 'What the fuck am I doing here? This is my wildest dream come true!'" He waits a beat. "And then I found out I had my brain tumor."

Ruffalo was diagnosed with an acoustic neuroma, a walnut-size tumor behind his left ear. He first suspected he had one after he had a dream about having a brain tumor, and when he went in for a CT scan, the doctors told him he was right. They said they could operate, but there was a 30 percent chance he might lose the use of the left side of his face. To complicate things even further, Sunrise was about to give birth to their first child, Keen, and Ruffalo didn't want to stress her out.

"He didn't tell anyone for weeks," his mom recalls. "When he finally did, I was like, 'Oh, my God. How could you bear all that?'" A week after Keen was born, Ruffalo broke the news; two weeks later, he went in for the surgery.

"I was certain I was going to die," he says now. But what terrified him the most was the idea that Keen might grow up without a dad. "I made a tape for him," Ruffalo says. "For when he was old enough to understand. Just saying, Hey, this is who I am."

The tumor turned out to be benign, but the surgery rendered the left side of his face almost totally paralyzed. Ruffalo went into hiding for months. He wouldn't take calls, wouldn't talk to anyone. He lost his equilibrium and started falling down a lot. One time he got lost for hours, two blocks from his apartment. He was at the peak of his career, with a newborn son – and he wasn't sure if he would ever work again, or even function.

As it turned out, Ruffalo made a full recovery, but the tumor was a mere prelude to another tragedy. On December 1, 2008, his little brother, Scott, was murdered at his home. Ruffalo was a popular hairdresser in Beverly Hills. A toxicology report found trace amounts of cocaine and morphine in his system. But police determined that he had been shot, as news reports put it, "execution style." A key witness who was also in the house was later reported to have died of a drug overdose, and to this day, the case remains unsolved.

Back when they were living together, Ruffalo says he sometimes felt like Scott was the older brother, not the other way around. He'd loan Mark money to get his car out of impoundment or give him pep talks about getting his life straight. "I was the actor who was pushing 30 and still doing 30-seat theaters," he says, "and he was the mayor of Beverly Hills. For years, people would meet me and go, 'You're Scotty Ruffalo's brother? I love your brother. He's fucking amazing.'"

At the time of Scott's death, Ruffalo had seen the script for 'The Kids Are All Right' and noted how much the character reminded him of his brother: "His charm, his spirit, his sense of humor, his daring. How great he was with women. How he sort of devoured life." He decided to make the role an homage. "I'm only capturing a tiny glimpse of him," he says. "But I think it ended up honoring him in a really nice way. He's a beautiful guy." He pauses. "He was a beautiful guy."

Ruffalo says that for a long time, he felt guilty about Scott's death. "You always wonder, What could I have done differently? But there's also the healthier part that says, You integrate it, and you get on. You never get over it; you just get used to it. You get calloused, a little bit harder maybe, so be on guard for that. But take these tragic things and turn them into something meaningful and worthy of the loss. Make it count. From here on out, do the best you can to make it count."

Ruffalo met Sunrise in 1998 in L.A., literally on the street. He was walking with a mutual friend of theirs, whom Ruffalo suspects had intentions of his own. "I don't think he wanted us to meet," he laughs. "But I saw her and was like, I'm going to marry that girl."

Ruffalo says the courting process "took some doing." "All I had was my decency, wit, and charm – I didn't have anything. When I met her, she was like, 'You don't have a driver's license, you don't have a credit card. What is wrong with you, dude? I can't be with you!' I was living in a converted garage, and she was there for that, she was game. She believed in me. She was like, 'I know you're a really good actor,' and I was like, 'You haven't really seen me act yet.' And she was like, 'I just know it, I can tell.'"

These days, the Ruffalos spend much of their time at their house in Callicoon, New York, a little town on the Delaware River two hours from Manhattan, population 167. Ruffalo first went up there in the mid-1990s, when one of his actor friends took him to visit the plot he owned. "It was amazing," he recalls. "I was like, 'How the fuck did you do this, man? Did your dad give you this?' And he was like, 'No, I just saw it, and I bought it.' And I was like, 'Holy shit! And you own it? I could do that!'"

Ruffalo was 28 when he bought his house, a one-room cabin on 27 acres for $63,000. Nowadays, Callicoon is his sanctuary, but back then, it was his fallback plan: Plan B, in case he washed out as an actor. "It was not a bad fallback," he says. "My mortgage was 600 bucks a month. If worst came to worst, I could get a job up there and be OK." Ever since he could remember, he'd had this irrational fear that he'd wind up homeless. Now he could stop worrying. "I have a place to go," he remembers thinking.

After Ruffalo got successful, he and the family kept going up there, and eventually got their current place, a big house on an old dairy farm with a 1953 John Deere tractor and a 19th-century post-and-beam barn. "Smartest thing I ever did," Ruffalo says of moving upstate. "It ended up having a huge influence on my life in many ways," he says. "Like the whole environmental thing – I'm not sure that would have gone down the way it has." He's referring to his status as the most visible face of the antifracking movement. He's spoken out on the issue at rallies and public hearings and on 'The Colbert Report'; he's even lobbied President Obama about it. "But my real baby," Ruffalo says, "is renewable energy. I feel like whoever starts to crack this nut is going to have a pretty clear shot at the White House. It's a $2 trillion business that America's being left out of."

For a few years the Ruffalos were splitting their time between upstate New York and L.A., where they had a house in the Hollywood Hills. But after his brother was killed, he had an epiphany: "The summer was winding down, and we were getting ready to go back to Los Angeles. In L.A., we were always in our car, we had this huge mortgage, like 10 times what it is in New York. And then we have this place upstate, which I love, our home. Sunny and I were looking at each other like, It's good to get to know you again, we're so happy here. And I was like, What the fuck are we doing?"

Ruffalo realized he was basically taking every job that came along in order to support their L.A. lifestyle. "And my kids were growing up without me." And so, in a single afternoon, he and Sunrise decided to sell the house in L.A. and move to Callicoon full time. They left the kids with their longtime nanny, flew back to L.A., packed up the house, put it on the market, and drove a U-Haul back across the country. "Within four or five days," Ruffalo says, "our whole lives changed."

Ruffalo has built a woodworking shop that he used to make Sunrise a bookcase, and has also dabbled in bow hunting. Lately he's been getting into welding. "Bikes. Lawn mowers. I built a chicken coop a few years ago – that was cool." Sadly, that coop was lost in what's gone down in Ruffalo family lore as the Great Chicken Coop Fire of 2010. It started one cold February night when a chicken knocked over a heat lamp inside. "It was just ashes," Ruffalo says of the aftermath the next morning. "The wheels were completely melted off."

"I was fucking devastated," Ruffalo says. "It was so sad." He starts to giggle a little, because he's talking about chickens – but you can tell he also means it. "There were like eight chickens in there, and I loved them, I really did. We raised them from chicks. That was a bummer, man." Still, Ruffalo would not be daunted. "I was like, 'We can't let this beat us,'" he says. "The chickens would want us to rebuild." And so he took his welder and built a new coop – this time with a solar heater.

For a while Ruffalo wanted to get some alpacas, but he says Sam Shepard talked him out of it – which is a pretty awesome thing for Sam Shepard to talk you out of. ("He was like, 'Uh-uh, don't do that. They're mean as shit.'") He did, however, get some rabbits. "We ended up giving most of them away," he says. "But we still have one left. As far as animals go, they're pretty chill. It's hilarious to see a rabbit hopping around the house."

But by far Ruffalo's favorite thing about the property is his garden. He spends nearly all his time out there. "In my underwear and a ratty shirt," he says, "barefoot and covered in mud and rabbit shit." He has "strawberries, rhubarb, tomatoes, basil, corn. A beautiful asparagus bed that's five years old. And watermelon, which is hard to grow up here. Now I'm doing a little orchard – raspberries, honeycrisp apples, blueberries, a pear tree. My wife is like, 'That fucking garden, man. It must cost $100 a strawberry!' But I don't care. That's my hobby. I like that."

The next night, Ruffalo and I stop in at a restaurant across the street from his apartment, where he orders mint tea and tapioca pudding. He just came from a long day of work, rerecording lines for Now You See Me. ("It was mostly action-movie stuff," he says. "Like, 'Wait, stop, freeze!' Or, 'Agghhhhhh!'") In two days, he and the family are leaving for Costa Rica – their second vacation in 12 years – and he still has errands to run. When he gets back, he'll start shooting Infinitely Polar Bear, a low-budget flick he's been trying to get made for three years; only now, after his Oscar nod and Avengers fame, he can.

Ruffalo is doing that a lot right now – making movies he loves that might not get made without him. This September he'll appear opposite Gwyneth Paltrow in a black comedy called 'Thanks for Sharing,' where he stars as a recovering sex addict. Then he'll star in 'Foxcatcher,' the wrestling movie, training for which Ruffalo calls the hardest thing he's ever done. "I'm usually 154, and I went up to 178," he says. He flips through his iPhone to find a photo of himself clean-and-jerking six plates: "I was yolked," he beams. Then he scrolls to the next photo, a close-up of himself in costume, with bald-cap makeup and yellow teeth. He laughs: "Sunny was like, 'We won't be having sex for a while.'"

Later this year, Ruffalo will strap on the green suit again and start work on a new Avengers movie. He loves playing the Hulk – especially because it's not as easy as it looks. "It's a tough nut to crack," he says. "You're spending two hours with a guy who doesn't want to do exactly what everyone came to see him do." But in the end, the key turned out to be simple. "We had to let Banner age," he says. "When you get to be a 45-year-old man, you start to realize: I know who I am, and I know who I'm not. I know my shortcomings, I know my strengths; maybe some of my shortcomings are my strengths. You start to face yourself as you truly are. And I think that's what Banner's doing. He's been running away from his life for 20 years, and he's realizing, 'I'm sick of running. I'm going to turn and face myself.'"

It's not lost on Ruffalo that he's talking about himself, too. "Over the past five years, my life's gotten a lot bigger," he says. "I'm feeling really free. I don't have to be a leading man. I can be a character actor. That's really what interests me anyway."

And after a life so filled with ups and downs, he knows there's not much point worrying, regardless. "It's been up, down, and sideways for me, man," he says. "I could become a huge star, or I could get cancer tomorrow. Shit happens. But at this point, I feel I'm starting to get close to the peak: In five or 10 years, I'll be peaking out and I really want to enjoy it while I have it."

But first, he has to make it back from Costa Rica. "I hear it's amazing," Ruffalo says. "They don't have a standing army, so they have one of the best school systems in the world. They get 92 percent of their energy from renewables. I'm telling you, Americans are going to be sneaking across the border into Costa Rica someday." His eyes start to come alive. "I'm so excited to go," he says, and all of a sudden it sounds like Sunrise might have another impulse move on her hands. Ruffalo starts to laugh. "Baby?" he says, pretending to look imploringly across the table at her. Ruffalo laughs. "What do you think?!"