Everyone loves Lucy and Ricky. But what’s it like being the Mertzes?

Most actors have to build a rapport. J.K. Simmons and Nina Arianda had to create antipathy.

In “Being the Ricardos,” writer-director Aaron Sorkin pulls back the heart-emblazoned curtain from “I Love Lucy” to reveal the fictional inner workings of the hit show that Lucille Ball and Desi Arnaz created. Nicole Kidman and Javier Bardem star as Ball and Arnaz, a pair of brilliant minds in a tempestuous relationship. But there’s another duo in on the act: William Frawley and Vivian Vance, who embodied the ever-bickering neighbors Fred and Ethel Mertz. As played by the Oscar-winning Simmons and Tony-winning Arianda, that onscreen sniping was just the half of it. Off screen, those original iconic actors despised each other.

“That was a complete surprise to me,” says Simmons. He and Arianda are in town from New York and New Jersey, respectively, sitting together on a couch in a West Hollywood hotel suite. Says Arianda, “But I think in a way, it really helped fuel their performance, because they are cantankerous as a couple, and the jabs felt very real.”

Arianda and Simmons had acted together, sort of, on Amazon’s “Goliath,” before landing their roles on “Ricardos.” “The whole time [on ‘Goliath’], I was like, ‘I don’t get to do anything but glare at him in a courtroom,’” Arianda recalls. That glare is front and center in the Sorkin film when we first encounter Vance and Frawley at a table read during a fateful week on the “I Love Lucy” show, and emotions only escalate from there. “It was really fun to play the more antagonistic scenes with this one,” says Simmons, nodding toward Arianda.

First they had to overcome their trepidation at playing those famous faces. “Terrified,” is how Simmons puts it. Sorkin reassured them that the biopic was “a painting, not a photograph,” Simmons says. “The onus was off to be Rich Little,” which was a big relief. Says Arianda, “Having that permission from the beginning relaxes you into seeing more things than you would if you’re just looking at something from a technical, tight perspective.”

When the writing is as good as Sorkin’s, Simmons says, everything they need is on the page. “Nina and I both come from the theater, as does Aaron. To have that, more than a framework, a completed house built there for you so that all you have to do is walk in the front door, is so confining and freeing at the same time, in a way that film scripts — even really, really good film scripts — rarely are.”

The actors didn’t have to play only Frawley and Vance; they had to re-create the Fred and Ethel characters as well. “To me, honoring the physicality was very important,” Arianda says. “Obviously, I had plenty of footage of Ethel, but I had a very difficult time finding anything on Vivian, and that was really troubling me.” Until she saw a clip of Arnaz introducing the cast to the live audience before an episode. “Here comes Vivian, she’s so aware of her hips, so feminine, walking like a dancer, shoulders back, head up and she bowed like she’s from the theater.” Vance’s Ethel, by contrast, had “this squared energy. I was like, now I can play and explore and try to be a better-tuned instrument for Aaron.”

Javier Bardem, left, J.K. Simmons, Nina Arianda and Nicole Kidman star in “Being the Ricardos.”

(Glen Wilson / Amazon Content Services)

Costume designer Susan Lyall gave another big assist. The foundation garments in particular were crucial in creating Arianda’s character’s posture. “What Susan brought to the table was life-changing for me with the character.”

Adds Simmons, “Usually for me with the wardrobe it’s like, ‘Which plaid shirt do you want me to wear?’ This was probably the most collaborative I’ve felt with the costume designer in my entire career. Again, it took me back to the theater, because I always found that important when I was doing a play.”

At one point for Vance, the wardrobe even becomes a plot point, not to be disclosed here. “What I can say is that Vivian is wrestling with how she perceives herself, and then how others see her and where they want her to stay for their own comfort,” Arianda says.

Vance and Ball were best friends, so making their relationship feel lived-in was key. “Nicole is a really, really generous actor, on and off screen,” reaching out to Arianda before shooting began. They read through scenes together, forming a bond they could use on set. During one intense scene between Ball and Vance, “that thing happened that you always want to have happened, where you lose yourself for a second. We both felt that. When they called ‘cut,’ Nicole grabbed my hand, and she goes, ‘There they are’ [of their characters]. That was very special because, for a moment, you get to step into the shoes that you’re hoping to honor.”

“I assume that was one of the moments that Bill came in and ruined,” Simmons says of his character. Arianda nods. “Correct.”

Playing on the meticulously replicated “I Love Lucy” sets was another thrill. Simmons couldn’t get over the original 1950s cameras. “All of those kinds of details were so brilliant.”

“I’ve never been to Disney World,” says Arianda. “But I assume that that joy and wonder you feel there is what that must be like, because I felt like my best 4-year-old self, with that absolute wonder, and you just get enveloped in it. It was really magical.”