For Mark Ruffalo, preparing for a role isn’t rocket science. To play an ophthalmologist in this year’s Blindness, he met with ophthalmologists. For Zodiac (2007), to play Dave Toschi—the San Francisco detective who investigated the murder of cab driver Paul Stine—he met with the real-life Dave Toschi. To play a bumbling brain-erasure technician in Eternal Sunshine of the Spotless Mind (2004), all he did was picture a guy “sitting alone in his bedroom in his underwear playing the bass—trying to play along to Clash songs.”

“I just want to look like I’m competent out there,” he told us last month at the Toronto International Film Festival. “If I was playing a vampire, I wouldn’t sleep in a coffin. I don’t take it to crazy extremes.”

But how do you prep to play a con man? To get ready for The Brothers Bloom—an entertaining if derivative shell game that opens the Chicago International Film Festival on October 16—Ruffalo talked to his friend, a former diamond thief. “He was one of the most exuberant, kind of fantastical people that I’ve ever met, with these great stories and the love of life…. I [thought], Oh, this is how these people are,” he recalls. “They are able to make even the most mundane things exciting.”

Ruffalo seems to have a penchant for glum roles: He’s played the ne’er-do-well brother in You Can Count on Me (2000), a philandering husband in We Don’t Live Here Anymore (2004), the guilty hit-and-run driver in Reservation Road (2007). But in The Brothers Bloom, Ruffalo plays the more lighthearted half of a con-artist duo: Stephen, the smirking bon vivant who persuades his reluctant brother (Adrien Brody) to pull off one last con.

It’s a role that requires Ruffalo to show off his playful side, as opposed to his characters’ usual obsessive, introverted or—as he puts it—“fastidious” qualities. Indeed, it’s probably the first Ruffalo role in which he comes across as the most boisterous person in the room. “How do you get someone’s confidence?” Ruffalo asks rhetorically. “How do people do that? By being confident. ‘Don’t worry—it’s completely taken care of.’ Everyone has that person in life that can talk them into doing anything, at one point or another, you know? You always feel slightly more alive with them.”

That feeling of being sucked in—of allowing yourself to be conned—may be what makes con-game movies so engrossing. By Ruffalo’s own admission, The Brothers Bloom is more frivolous than his average film—it’s a fast-paced caper comedy that unavoidably conjures comparisons to Wes Anderson. It includes the whimsical details (Rachel Weisz, as Penelope Stamp, the heiress the Bloom brothers plan to con, says her hobby is to “collect hobbies”); the deliberate blurring of time frames (the movie’s prologue seems set around the era of Jesse James, but the plot involves car crashes and cell phones); the use of Cat Stevens on the soundtrack. But peer deeper and you can recognize the sensibility of sophomore feature director Rian Johnson, whose densely plotted, high-school–set Raymond Chandler homage Brick (2005) also hinged on a thicket of double-crosses and competing motivations.

PICK A CARD Adrien Brody is going to need some convincing.

Photo: Jeff Vespa/WireImage

Ruffalo plays the second-banana role to Brody, whose character’s trust—or lack thereof—in Stephen and Penelope is the driving force of the movie. But the size of the role doesn’t faze Ruffalo. “A great role is a great role, you know?” he says. “I don’t have much ego about where my positioning is in movies. It kind of goes for me—you know, what’s the character and the story, who are the people involved, where are we going to shoot, and how much am I going to get paid, in that order.”

Those are modest criteria for an actor whose breakthrough role—as the returning brother in Kenneth Lonergan’s You Can Count on Me—earned him comparisons to the young Brando. It’s an association Ruffalo finds amusing. “There’s only one of those guys,” he says. “It was a nice comparison to have out of the gate, but he’s a pretty big actor to live up to in any way.” He may not be Brando, but if anything, Ruffalo’s star has only been rising ever since the Kenosha, Wisconsin, native cut his chops on Los Angeles and New York stages in the early ’90s, with a smattering of roles in independent movies and television. His stage collaboration with Lonergan (notably in 1996’s This Is Our Youth) eventually led to his casting in You Can Count on Me. (His lone Chicago performance was in Eric Bogosian’s Griller at the Goodman in 1998.)

At Stella Adler Conservatory in L.A., he learned to see acting not only as a craft but as a means of exercising social responsibility; it’s a message he’s extended into his personal life by being vocal about his politics—even his more out-there politics. He reportedly contributed to both Mike Gravel’s and second-choice Dennis Kucinich’s campaigns, telling the Los Angeles Times he was “shocked by [Gravel] but also inspired by his independence.” (He’s voting for Obama now.) And although the play it got on the Internet may have been disproportionate to his remarks, he thinks the government investigation of September 11 fell woefully short—and he is surprisingly eager to expound on the topic. “When you look at it, when you read about it, we only spent $3 million on that investigation, and we spent $60 million on investigating President Clinton’s indiscretion,” he says. “Now there is something wrong there.

“Do I think there’s some vast conspiracy?” he asks, after rattling off a litany of things he finds suspicious, including the idea that there was “gold missing from underneath those buildings.” “No. I’m not sure, but I want to know what’s going on.”

Ruffalo’s roles aren’t expressly political, but he tries to make each performance count—even more so, he says, after surviving a brain tumor in 2001. He sees stage acting and screen acting as fundamentally similar, and he disagrees with the Hitchcockian notion that film acting relies more on how a scene is shot than on motivation and character. “Yeah, sure, you could just stand in the frame and say your lines and let the filmmaker move the camera to tell the story,” he says. “But if you don’t have a good actor, it doesn’t work as well as if you have Henry Fonda, who’s a great actor, and all of a sudden it has an extra added dimension.”

That’s sort of the principle of The Brothers Bloom: Ruffalo brings an added poignancy to a part that risks being subsumed in the gearwork of the plot. “It’s a departure for me in some ways,” Ruffalo says. “A lot of the stuff I do is usually a little bit deeper or heavier or I’m dealing with more difficult issues. This is just one of the other sides of the same coin—of entertaining people and taking them on a fun ride.”

The Brothers Bloom opens the Chicago International Film Festival October 16 and is scheduled for release in Chicago January 16.

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