The character of Christian in the social comedy The Square appears to be a sexist, racist snob.

But the actor who portrays the art museum director thinks Christian is anything but a bad person.

"He is a good guy. He has his heart in the right place and he wants to do good," says Danish actor Claes Bang, 50.

In the film, winner of the Cannes Film Festival's highest award, the Palme d'Or, Christian is preparing for a major exhibition at his prestigious Stockholm museum when his wallet and phone are stolen.

In trying to get the items back from some of the city's poorest residents, and in his meetings with American journalist Anne (Elizabeth Moss), his inner self is shown to be at odds with the arts-loving, liberal-values outer man.

"He's got a blind spot somewhere. He talks about high ideals - about how we should love each other, take care of each other - but is the opposite in real life," says Bang, who was selected by Swedish director Ruben Ostlund after a Europe-wide search for an actor who could portray the urbane but flawed Christian.

"We all try to be decent citizens, but we can't live up to our high ideals. That's why people connect with the film," he says.

Director Ostlund likes actors who can improvise and, in one pivotal scene, Bang and Moss, having just had sex, are in bed, fighting over the used condom.

He insists on keeping it, an act that offends her because it implies that she might impregnate herself with it. They tussle over the rubbery contraceptive.

Ostlund had the actors repeat the fight over a dozen times, with variations in intensity. It might sound as if Ostlund was searching for the funniest, most extreme version of the argument, but that would not be true, says Bang.

"If we were aware of the humour in it, it would not be funny.

"It's funny because, for Christian, it's a matter of life and death. He's scared because he has two kids and he doesn't want any more."

"From the realism comes the humour and the fun," he says.

In between the comic moments, The Square - which has a run time of 151 minutes - has odd, hallucinatory beats, when it is not clear if something is actually happening or if Christian has imagined it.

Story threads are also left unfinished on purpose.

"Ostlund wants you to ask the questions and there are no answers. He wants to leave the audience hanging, asking 'why is that?', 'what was that?'.

"So many people ask me about what happened to this character or that one. But this is life... We are so used to movies where we get the answer to every question. There are no answers."