Mark Ruffalo has appeared in more than 30 movies without falling into a typecasting trap.

The 39-year-old actor, who spent his formative years in the theater, made his big-screen breakthrough in 2000's You Can Count on Me opposite Laura Linney. He's had supporting roles (Collateral, Eternal Sunshine of the Spotless Mind) and tried his hand at more mainstream fare, playing opposite Reese Witherspoon in Just Like Heaven.

Zodiac isn't making it any easier to pin Ruffalo down. As a member of a large ensemble cast, he portrays David Toschi, the San Francisco homicide detective who spent years tracking the Zodiac killer who terrorized the San Francisco area beginning in the late 1960s.

Making the film was the kind of experience that might have driven some actors around the bend; the movie's perfectionist director, David Fincher, reportedly called for a patience-taxing number of takes.

"He's very thorough and thoughtful," Ruffalo said of Fincher, best-known for movies such as Se7en and The Panic Room.

"He's one of those people who expect other artists to pour themselves into the work as much as he does. . . . I hear the whining going on, but I don't understand it. Some of it comes from people who are not as prepared as they should be."

So who might that be? "Whoever's whining the most," he says with a chuckle.

"We get paid really well. The craft-service person on the film works 50 times harder than we do. Besides, there's just so much more you can say positive about Dave than how many takes he makes you do. "

Still, working on a Fincher movie requires adjustments.

"You have to change your style a little. If you're working in a long dialogue scene with a dolly shot, you know it's going to be 12 takes before everyone is up and running. You know you're not going to get the pitch you want until maybe the 13th take. And you know that the 10 takes after that are going to be the sweet spot."

Zodiac, which also stars Jake Gyllenhaal and Robert Downey Jr., might be as difficult to classify as Ruffalo. It's a police procedural, a thriller and a newspaper movie. On top of that, it offers no slam-bang conclusion. The case caused many careers to rise and founder, and The Zodiac was never apprehended.

"That's one of the most exciting things to me," said Ruffalo. "David was playing with the expectations of the genre. What I sense in screenings is that you actually experience what the people who lived with this thing experienced - the frustration, the satisfaction of getting clues and the satisfaction of coming into contact with the person who's the best suspect. The payoff is the mystery."

Ruffalo had the advantage of spending a couple of days with the man he played. "The case brought a lot of crazy people out of the woodwork," he said, referring to the fact that The Zodiac sent letters to the San Francisco Chronicle and other Bay-area papers. "David (Toschi) told me he met with thousands of people who said they knew who the killer was. He became very quick at debunking them.

"I asked why he talked to Robert Graysmith (the former San Francisco Chronicle cartoonist who wrote two books about the case and who's played in the movie by Gyllenhaal). He said he saw that he was sincere and that he cared as much as he did."

Ruffalo's glad that audiences have trouble squeezing him into a mold. "I feel lucky, man. If someone had asked me 20 years ago if I was going to be able to do what I'm doing now, I would have laughed at them. I feel fortunate because of my theater work and how long it took me to get where I am now."

Where is he now? He's a successful actor and a husband with two children (a 5-year-old boy and a 2-year-old girl) and a third child on the way.

"My path has taken me down some difficult roads and some easy roads. Because of all that, I have a sense of what good material is and what's interesting for me to do."

On the horizon

Upcoming roles for Mark Ruffalo:

• Margaret reunites Ruffalo with director Kenneth Lonergan (You Can Count on Me). It's the story of a teenager who fears she may have caused a bus accident.

• Reservation Road teams Ruffalo with Joaquin Phoenix and Jennifer Connelly in a Terry George (Rwanda) film about repercussions from a hit-and-run accident.

Robert Denerstein is the film critic. denersteinb@RockyMountainNews.com or 303-954-5424