Mark Ruffalo is sitting alone in the back of Victor's Deli in late afternoon sun, a weekday, the place dead. He is wearing a blue velour jacket, jeans and a loose, white button shirt. The silver chain around his neck holds a St. Christopher medal, patron saint of protection. He is rumpled, hair and clothes, like he just came out of the dryer. He waves hello.

Not too long ago, during the decade he spent as a struggling actor in Los Angeles, this was the kind of place where Ruffalo punched a time clock. He was a busboy at the faux-'50s malt shop Ed Debevic's, where 10-year-old girls like to have their birthday parties, the Beverly Hills version of Chuck E. Cheese. He was a waiter, doorman, caterer, bartender at a series of now-shuttered watering holes where he slung martinis and Midori cocktails to the Hollywood swells. He also painted houses. And dug holes and stuck plants in the ground, and thought a lot about going back to Wisconsin to work for his dad, where he would make a new life sandblasting water towers.

He acted in more than 30 plays over 10 years. At the bars he worked, Ruffalo would hand fliers to customers; they never came to see him on the stage. "You're totally invisible," he remembers. "You're just a conduit between them and a drink. Like a drug dealer. Of course, 99 percent of what people say in bars is absolute crap. Girls come to understand this rather quickly."

Ruffalo laughs; he laughs a lot, a slurry heheheheh. It is a good thing he didn't quit because now he is one of the most interesting actors working in Hollywood -- appearing currently in both the Michael Mann thriller "Collateral" and "We Don't Live Here Anymore," an intense film based on the short stories of Andre Dubus, opening in Washington on Friday, in which he cheats on his wife (Laura Dern) with his best friend's spouse (Naomi Watts).

Maybe because he was trained in the theater, Ruffalo, 36, can actually act, and his work in even mediocre films is often singled out. He repeats a mantra: You serve the material. He possesses the craft to disappear into his characters, and some of them are not very appealing, but they are not dull.

Ruffalo -- say "rough," not "roof" -- broke into the public consciousness by going east, earning an off-Broadway rave as a slouchy, funny, nihilistic brat in Kenneth Lonergan's play "This Is Our Youth" in 1997. A New York critic compared Ruffalo to a young Marlon Brando. That's the kind of press that changes a career. Ruffalo followed it with the lead in Lonergan's film "You Can Count on Me" (2000) for his turn as Terry, the sweet and infuriating slacker, muddle-headed but big of heart, a boy-man, lost but redeemable. The kind of man women cook eggs for in the morning. After that, in quick succession, he worked beside Robert Redford in "The Last Castle" and Nicolas Cage in "Windtalkers."

Then, just as he began to orbit, Ruffalo plunged back to Earth. It was almost like a movie: The talented young man had a dream, a very bad dream, that something was growing inside his head. And when the surgeons laid him out on the cold table, and opened his skull, they found that he was quite right. He had a brain tumor that was, mercifully, pronounced benign. He is okay now. But he is also a changed man. And, he thinks, probably a better artist for it. But what a way to learn.

He orders lemonade with ice tea. "I can't bring myself to call it an Arnold Palmer," he says.

He comes from a family of hairdressers: mother, two sisters, a brother. Stylists all. His dad, divorced from mom, runs a commercial painting company. To describe Ruffalo as good-looking doesn't do it. He is handsome in the Italian way, lean and lithe and hairy, dark meat to Brad Pitt's white, with a Roman nose and a full mouth and emotive eyes that, in his movie roles, register confusion and wound and hunger.

"For all those years it felt like Los Angeles just didn't get me," he says. "This one casting director told me they don't look for guys like you out here in L.A. They look for guys like you in New York. I don't know. My look or quality. Out here, maybe episodic TV turns out a beautiful, easily accessible type. I was blue-collar street-fighter type. The darker tones, you know? That's what they said." He pauses and seems to think about that last statement. "Although you never really know what anybody is talking about. That's one of the problems with language."

In his press clips, he is often referred to as the thinking woman's sex symbol, and in his role as the New York detective in Jane Campion's kinky "In the Cut" (2003), he gives good reason for the rep when he sets upon co-star Meg Ryan like a starving man at an all-you-can-eat buffet.

He was born in Kenosha, a little burg in Wisconsin. His father was kind of a schemer-dreamer, and the family moved first to Virginia Beach, and then to the margins of San Diego, which Ruffalo remembers as not the sunny Republican idyll but a tough beach town filled with burnouts and crystal meth. As a teenager, Ruffalo was more skate punk than drama club, raised on the Dead Kennedys, Circle Jerks and the Clash.

Ruffalo didn't go to college; he went instead to the Stella Adler Academy, the well-regarded acting school in Los Angeles that trained Robert De Niro and Chris Cooper. It is a three-year program; he spent six years with Adler and paid for his classes with work-study. He spent the extra years "really just hiding." He says, "I cleaned toilets." Benicio Del Toro was the star pupil.

Ruffalo does a nice imitation of his mentor, now deceased. "Natural is boring, darlink," he mimics Adler. "Never pull the character down to your level. You lift yourself up! Don't be small don't do it, darlink. You must serve the material."

Ruffalo estimates that he went to more than 800 auditions over eight years.

"I wasn't getting anything. I tried for voice-overs, commercials, TV, everything," he says. What he eventually got was a Clearasil commercial. Then he won a couple of parts in little horror movies. They were not good films.

"It is so hard. Not a good job for depressives. For manics it's okay. I'm really envious of the manics," Ruffalo says. "I only got one-half of the equation."

His talent agency dumped him. "I wasn't making them any money, so who could blame them?" he says. "I was doing whatever I could to get before a camera, even to the point of lying to do a non-SAG, nonunion movie so I wouldn't get bounced out" of the Screen Actors Guild. "But I got thrown out anyway because I didn't pay my dues for two years. I went to them and threw myself before the board: Man, I haven't been working. I'm starving. I'm depressed. They were like, cough it up."

Los Angeles is filled with pretty men with head shots. Ask any waiter. Ruffalo must have thought of quitting. "All the time," he says. "A lot of times where in the darkest night of the soul, you wanta give up everything. You work so hard, it means so much, and so little return, or encouragement, and you're just, screw this, I can't go on like this. It's too hard on me. Something about it, it's maddening. I mean, you go a little crazy from this total absolute wall of rejection."

But Ruffalo kept working in his little plays. Twenty people in the audience, half of them friends. Casting directors would promise to come, then blow him off. He wrote; he directed.

He says he is not bitter.

"Frankly, I probably wasn't very good at that time, so there was probably a reason I wasn't getting parts," he says. "I often think back to what would have happened if I had gotten all the things I wanted. I wouldn't be the actor I am today. I tell you, it was 10 years of acting before I began to have any sort of -- I don't know really -- interesting stuff going on in my work. It was only out of really difficult times that I grew the really deep roots I needed to be the actor I was hoping to become."

He never experienced headaches, blurred vision or problems with balance. There was a slight, almost imperceptible loss of hearing in his left ear. He was newly married to the French actress Sunrise Coigney, and they had a baby, Keen. One night, "I dreamt I had a brain tumor, of all things. It was such a real dream, I followed up on it, and wham, bam, thank you, ma'am," he says. "I thought that was it for me."

The doctors scanned his head and found a mass. The operation lasted 10 hours. He reacted badly to the anesthesia. Six months of recovery. He lost 40 pounds. An additional 10 months before he worked again, in "In the Cut."

"All these crazy things go into it when someone tinkers with your brain. What if they took away something important, that was talent? What if that was what made me special? I wasn't sure I still had it."

The experience changed him, Ruffalo says. First of all, it was terrifying. In many interviews now, the actor declines to talk about it, saying he doesn't want to be seen as some kind of medical miracle. "But it is part of my life, you know? A big part," he says.

What the tumor did, "it focuses your attention and your intentions. It makes you aware of a lot more. The choices. The way you appreciate things." He says the tumor made him focus on what he wanted to do with the rest of his life. "If, you know, I survived and everything." Then the laugh again, heheheheh, and he exhales a long, drawn-out expletive.

In the last few months, Ruffalo has appeared on-screen as the dreamy boyfriend of Jennifer Garner in the frothy "13 Going on 30," as the tech geek bouncing on the bed in his Homer Simpsons with Kirsten Dunst in "Eternal Sunshine of the Spotless Mind," the cop Fanin in the noir "Collateral," and now as the cheating heart in the almost-too-real '70s-style drama of marital strife "We Don't Live Here Anymore."

Ruffalo chooses roles based on scripts. "And that's all you have to go on, as an actor. How it reads." He says, "It's funny now, because I would bet that most people who know me would think of '13 Going on 30.' " He shrugs. He liked the script because it reveled in a kind of innocence of youth. "People in this town will say, oh, Mark can't do comedy. Or Mark can't be a leading man. Or Mark can't get the girl." He plans to prove them wrong.

His performance in "13" was actually a challenge for him. "I usually play parts where I'm able to hide behind the character. I can disappear. But in that one, I was this nice, stable, normal, decent guy. And that was hard, man. I kept wondering, what do I do with my hands? Do I just keep them in my pockets?"

"We Don't Live Here Anymore" is more of a Ruffalo movie. Took 25 years to get made. "The subject matter scared them," Ruffalo says. Originally, Dustin Hoffman was signed to play Ruffalo's part -- back in the 1970s. "My first inclination was not to do it. Such sensitive material. I didn't know who the director was. We'd have a month of preproduction. No rehearsal time. I thought it'll be junk. This is insane."

The movie is brutal. There are scenes that may remind some couples of their worst moments; but there is also something almost funny in the struggles of these mortals. "These humans are raked over the coals," Ruffalo says. "Can two people come back from such painful misdoings? This season of infidelity? I felt it was an honest and mature look at marriage in crisis and everybody is afraid to make these movies nowadays, everyone wants to be entertained, to make things easy."

He was drawn to the piece for its challenge, for the chance to make a movie that is very much like the plays he spent his decade performing. "It's a script and it's acting. There's no tent pole, no set piece, no action sequence, no mystery, no suspense, and so I'm really proud of it as an acting piece. It had to be pitched just perfect."

Ruffalo slurps some more tea. "What I like about it here are these people. The characters. The actors. They're on the line. They're vulnerable, out there, in the moment, no safety net. And what they really have to do is count on each other."

Mark Ruffalo knows from struggle: He finally made it to movie screens after a decade, then brain surgery sidelined him."For all those years it felt like Los Angeles just didn't get me," says Ruffalo.Ruffalo and Naomi Watts in "We Don't Live Here Anymore," opening Friday.