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In this business you can easily watch up to 200 films in a single year. It's therefore no surprise that it's already hard for this pundit to remember all the films I caught at the Cannes Film Festival, which was less than one month ago. Of course, that doesn't mean some films don't stick with you. One film that made a lasting impression with me over the past 18 months was Maya Forbes' “Infinitely Polar Bear.” The autobiographical drama debuted at the 2014 Sundance Film Festival and is finally making its way to theaters this week.

Inspired by Forbes' relationship with her own bipolar father, the film centers on Cameron (Mark Ruffalo), a man trying to control his behavior after he unexpectedly becomes a de facto single parent to his two young daughters. Ruffalo has delivered many great performances over a storied career, but his work here is unlike anything he's ever done before.

Ruffalo, who has spent a good deal of time over the past year promoting “Foxcatcher” and a little movie called “Avengers: Age of Ultron” sat down with HitFix to talk about “Polar Bear,” which was filmed after Bennett Miller's Academy Award-nominated drama.

The two-time Oscar nominee says Forbes wanted the character to be authentic, but not a carbon copy of her own father. He notes, “She didn't say there was one particular thing that was important, but she wanted the essence of Cam, which I did, too.”

As for Cam's bipolar characteristics, Ruffalo confronted the dicey proposition of playing it truthfully without having the audience truly fear for the young girls' safety.

“I think you're doing a balancing act,” Ruffalo admits. “If you start a movie with him just completely zonk-bonkers, that will set the tone for the rest of the movie.”

For more on Ruffalo's thoughts on “Infinitely Polar Bear,” and whether he'll be making that rumored appearance in “Captain America: Civil War,” check out the video embedded at the top of this post.

“Infinitely Polar Bear” is now playing in New York and Los Angeles.