Susan Sarandon stars as heiress Doris Duke in Bernard and Doris, tonight at 8 on HBO.

Alison Rosa

NEW YORK — When Susan Sarandon brought her dog, Penny, along to a round of interviews at HBO last month, it seemed only fitting.

After all, Penny did have a couple of close-ups in Bernard and Doris, in which her mistress plays heiress Doris Duke and Ralph Fiennes is butler Bernard Lafferty, to whom Duke left millions. (The show airs tonight at 8.)

And Duke, like Sarandon, did love dogs.

“She was very big on animals, and treated her animals better than (she did) the people who worked for her, apparently,” said Sarandon, settling in to talk as Penny trotted away. “One of the lines (that got cut) was that she was yelling at one of her maids because the maid was reprimanding the dog for pooping in the house — because they were always just going everywhere — and she said, meaning the dog, ‘She lives here. You don’t.’ ”

Any resemblance between Sarandon and Duke probably ends at their fondness for dogs, since the actress, as director Bob Balaban acknowledged in a separate interview, “doesn’t look anything like Doris Duke.”

Also, in real life, Lafferty was more than 30 years younger than his employer. In Bernard and Doris, they might almost be contemporaries.

“We weren’t doing an impersonation, and we weren’t doing a biography, and no way did I want Susan to be 6 feet tall and look like Doris Duke,” Balaban said. “And Ralph was never going to be Bernard Lafferty because Ralph looks like a movie star and Bernard (didn’t). But we did things to them — Susan has blond hair, Ralph has a little tummy pad.”

Before taking the role, “I only knew headline stuff” about Duke, Sarandon said: that she’d posted bail for Imelda Marcos, wife of Philippines dictator Fernando; that Duke University was named after her family, “that she made her money into more money, whereas Barbara Hutton had lost all her money, ultimately. I knew ... that she had kind of an outrageous lifestyle.”

That’s why, she said, “I wasn’t as interested on focusing on those big events as I was in telling the story of two people with ‘trust issues,’  ” she said, laughing. Bernard and Doris is about “two people who were not very successful in relationships having the courage to reach out to each other, to become friends, and in a very deep way, loved each other,” she said.

“But definitely (they) were a funny-foot-meets-a-funny-shoe kind of unlikely couple. That was more interesting to me than the big gestures that most people know about,” she said. “So we weren’t interested in doing a biopic. This was kind of an anti-biopic.”

And in an anti-biopic, there’s freedom to imagine a relationship that might or might not have existed.

“This we were charting as a love story,” Sarandon said.

“How do they earn each other’s trust, ultimately, and the hits and misses and the rejections and the acceptances?” she added. “And I was eager to have a story where there was mutual caring, not just that he was obsessed with her. That seemed a little creepy to me.”

Not, of course, as creepy as the accusations, never proven, that Lafferty might have hastened Duke’s death.

Does Sarandon believe the relationship between the real Duke and Lafferty was really one of mutual caring?

“Let me put it this way,” she said, cutting to the chase, “I felt that if he wanted to kill her, he could have done it much earlier. He didn’t have to stick around that long.”

Besides, she added, “even when you read books, you don’t know how much of it is hearsay. ...You never know, even when you’re dealing with someone who is in the inner circle,” if they’re telling the truth, or even if they know the truth.

“I know from my own family — I have eight brothers and sisters — and when we sit down and talk about an event, you’d think we were all in different places at different times, depending on position in the family,” she said, laughing.