The

Henry VIII

that we see in

The Other Boleyn Girl

is a pretty piggy chap. Wed to

Catherine

, who can't deliver a male heir, the king of England struts around in search of a mistress. Enter

Mary Boleyn

, a nobleman's daughter. The monarch and the mistress bed, and a child is born.

And at the very moment Mary is in labor, along comes her saucy sister, Anne, who has been teasing and toying with the king's affections all along. Then and there, she offers herself to the Tudor titan.

"When you read this stuff on the page, you think, My God, how can he do this?" says Eric Bana, who had to figure out how - because, in The Other Boleyn Girl, he is Henry.

"You know, it's very melodramatic, and trying to make all of that stuff believable is a challenge," says the Australian, who stars opposite a couple of other non-Brits - Scarlett Johansson (as Mary) and Natalie Portman (Anne) - in the Justin Chadwick-directed period drama. The film opened Friday at area theaters.

"It just takes a lot of commitment on the day," he explains. "To make it believable that right at that point in time he's going to walk away from his son who's just being born, given the opportunity to be with this other woman. . . . You've got to really know your character."

"I found him intriguing," he adds. "I found a lot of his behavior justifiable - to the actor side of me. I enjoyed it. I tried to put myself in his shoes, wherever possible."

To that end, Bana, 39, read the Philippa Gregory novel The Other Boleyn Girl, which he deems "pretty accurate" in its history. But he also took on a good number of non-fiction tomes about Henry, his life and times. What the actor didn't do was watch other films featuring King Henry.

Richard Burton in Anne of the Thousand Days? No thanks. Robert Shaw's A Man for All Seasons? Ignored. Charles Laughton's Henry in Young Bess? Pass.

"I was bombarded by friends calling and saying, 'Oh, you've got to check out this version and that version,' " he says. "But I found the historical works far more useful than looking at other pictures, other people's interpretations. I always find that very dangerous.

"It's confusing enough, to be honest, when you've got this script that's being developed out of a novel which has come out of history, and then you have the second draft and then you have the shooting draft and then you have the rehearsal period.

"In the end you just go crazy and you can't remember what's what. So to throw another adaptation or another interpretation from another time just leads to despair."

Bana, who is of German and Croatian heritage, and who was born, and still lives, in Melbourne, has a small Australian film, Romulus, My Father, slated for art houses this spring. The story of a couple (Franka Potente plays the wife) struggling to raise their son, Romulus won best picture at the Australian Film Institute awards last year, and won Bana best actor, too.

Known for his work with Ridley Scott (Black Hawk Down), Steven Spielberg (Munich), and Wolfgang Petersen (Troy), Bana has made a couple of films since shooting The Other Boleyn Girl in the U.K. in late 2006. He stars opposite Rachel McAdams in the adaptation of Audrey Niffenegger's best-seller The Time Traveler's Wife, about a librarian whose ability to toggle back and forth through centuries puts a strain on his marriage. (Gee, what's the problem?)

And he's the villain, Nero, in J.J. Abrams' Star Trek, now slated for a 2009 release.

"I got to do a few weeks' work on that, a really great, fun script," he reports. About the multitasking Abrams, creator of TV's Lost and Alias series, and director of the best of the Tom Cruise Ethan Hunt franchise, Mission: Impossible III, Bana is all positive.

"He's very annoying, very talented," he says with a laugh. "I would like to rephrase that: He's annoyingly talented. Don't isolate those two comments!"

It was Chopper, a fierce little Aussie number based on the autobiography of convict Mark "Chopper" Read, that first brought Bana to Hollywood's attention. Since its release in 2000, Bana has worked nonstop. He says he turns down "a lot" of material, and only really has time to do two films a year.

"If you're doing cameo pieces, you can do a bunch, but most of the films I've done I've been there every day of shooting. And that can take it out of you."

Married, with two kids, Bana concedes that he's obsessive about his work.

"Yeah, I think I am. Most actors are. When you're working on a film, it's just the only thing you can think about, it occupies your every conscious thought. You just become a ghost again for a few months - you become that vacant, vague father and husband that my family knows so well," he says, with a chuckle.

"They wait there and dream of my return."

Thunderbirds Are Go! Today would be a good day to head to the Institute of Contemporary Art over on the University of Pennsylvania campus. That's because, in conjunction with the ICA's Puppet Show exhibition - a cool collection of 29 artists' work in various forms of puppetry - a double bill of classic puppet-centric cinema is in store.

Check out Gerry Anderson's Thunderbirds episode "Attack of the Alligator!" - a 1960s British marionette masterpiece - and also Godzilla, King of the Monsters!, the '50s sci-fi classic in which a 400-foot monster reptile (really just a little puppet) runs rampant across Tokyo.

For info, phone 215-898-7108 or visit www.icaphila.org.

Contact movie critic Steven Rea at 215-854-5629 or srea@phillynews.com. Read his blog, "On Movies Online," at http://go.philly.com/onmovies.