You know the season of the big, dumb summer blockbuster has ended when a film's director starts talking about existentialism and the influence that the chair of religion at Columbia University has on one of his key characters. Welcome to fall, and welcome to director David O. Russell's "I Heart Huckabees," which arrives in theaters Friday (October 1).

"Dustin Hoffman and Lily Tomlin are existential detectives who you could hire to investigate the meaning of your life," Russell explains. "They are formal, they wear suits, they are Paris-trained, and their clients include Jude Law, Naomi Watts, Jason Schwartzman and Mark Wahlberg. Their nemesis is Isabelle Huppert. Hilarity ensues."

The impressive ensemble cast fell into place when Dustin Hoffman signed on as one of the existential investigators. "Dustin Hoffman was the dream guy to play this part," Russell recalled. "He had been asking to speak to me since 'Flirting With Disaster.' When I made 'Three Kings,' I even considered giving him the [George] Clooney role. But I saw him running around in the fatigues in 'Outbreak,' and it didn't feel right."

Despite the big-name cast and heady subject matter, Russell kept the film personal by finding inspiration in his own life. "Bob Thurman, who was a teacher of mine in college, was the main inspiration for the Dustin Hoffman character," Russell said. "He's the chair of religion at Columbia University and happens to be Uma Thurman's dad. He always wore rumpled suits and was very unpretentious. Meanwhile, he's one of the greatest transcribers of Sanskrit and ancient texts in America."

Not even Thurman could help the "Three Kings" director fast-track "I Heart Huckabees" as Russell struggled with the complex story for years. "After I made 'Three Kings,' I knew I wanted to go back to making personal movies," he said. "That was one thing I learned from making that picture. I wrote a movie for Jason Schwarztman. I'd fallen in love with him from 'Rushmore.' I wrote for Mark [Wahlberg], who's a very close friend of mine, and for Lily [Tomlin] ... I wasn't satisfied with the story. It took 18 months to figure that out, which is why it's been five years since I've made a movie. Then I had a dream. I had a dream [that] I was being followed by a woman detective but not for criminal reasons. I wrote it down and I realized that was the conceit of the movie right there."

The inclusion of Wahlberg is no surprise, given the duo's work on "Three Kings." The two have remained friends since working on that acclaimed film, and they've continued to develop a creative relationship. "My friendship with him is like the friendship in the movie: He went to prison, and I went to college. Very different, but we still have a lot of love for each other."

But Wahlberg's Tommy — a firefighter struggling with his "hero" status — wasn't initially expected to play the major role that he does in "Huckabees." "Mark's character evolved a lot during the writing," Russell said. "At one point my co-writer thought we didn't have room for him, and it turned out to be one of the most interesting characters in the movie, I think. Once 9-11 happened, his character grew. He became a lot about my response to 9-11."

As a smooth marketing exec who lives with his spokesmodel girlfriend (Naomi Watts), Jude Law plays against leading-man type when his character hits an ugly rock bottom. "He's a good-looking boy, and he's talented. He's not a movie-star personality; he's an artist. I thought it was fun that the very year he and Naomi became these Oscar-anointed icons, they got to come to this movie and turn that upside-down a little bit."

Despite the A-list cast, bringing the film's blend of dark humor and a heavy dash of optimism to the screen remained an uphill battle. The film's an odd sell, even now that we're clear of popcorn-movie season, and Russell knows "Huckabees" is a bit of a gamble.

"I had a free ticket after 'Three Kings,' " he said, "and I decided to use it to take a risk."

Check out everything we've got on "I Heart Huckabees."

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