Being the Ricardos, written and directed by To Kill a Mockingbird playwright Aaron Sorkin, focuses on the two people that led what was perhaps TV’s most influential sitcom, I Love Lucy, by going behind the scenes to uncover how Lucille Ball and Desi Arnaz (played on screen by Nicole Kidman and Javier Bardem) were anything but Lucy and Ricky Ricardo, their beloved characters.

The film, which opened in movie theatres December 10 and became available for streaming on Prime Video December 21, follows a full production week on the classic sitcom, from the first table read to the final filming, all while the cast and crew navigate off-screen drama that threatens to upend everything they hold dear. Sorkin has imagined a timeline in which Ball has been accused of being a communist by Walter Winchell, Desi’s extramarital philandering has been exposed in a tabloid, and a surprise pregnancy is threatening to end the smash hit series just as it’s hitting its stride—all events that really happened, but in Sorkin’s screenplay, they’re all happening the same week.

WATCH: Go Behind the Scenes of Being the Ricardos With Nicole Kidman and Javier Bardem

But the film also pulls back the curtain on Lucy and Ricky’s best friends, partners in crime, and landlords—Fred and Ethel, originally played in the ‘50s by Broadway vets William Frawley and Vivian Vance. And to bring these legendary performers back to life, Sorkin chose two performers with substantial stage backgrounds themselves, J.K. Simmons and Nina Arianda.

“The one thing Vivian Vance is not is Ethel,” shares Arianda, a 2012 Tony winner for her performance in Venus in Fur. “Here’s a woman who was a leading lady. She was an ingénue, a very successful torch singer. She was a very desirable woman. She had her own perfume line at one point—that’s how popular she was.”

Arianda was able to draw on her own stage background after learning Vance’s stage past, which includes performances in the original companies of Kern and Hammerstein’s Music in the Air, Porter’s Anything Goes (Vance understudied Ethel Merman as a member of the ensemble), Arlen and Harburg’s Hooray For What!, a 1947 revival of The Cradle Will Rock, and more. Arnaz and the I Love Lucy team cast Vance in the role after seeing her in a production of Voice of the Turtle at San Diego’s La Jolla Playhouse.

But when we see her in Being the Ricardos, Vance has traded in her glamorous days as a leading lady to play the frumpy housewife and landlady Ethel Merz in I Love Lucy. Even just four years older than Ball, Vance’s Ethel was constantly referred to in Lucy scripts as being significantly older than Lucy, and her on-screen husband Fred would regularly make potshots about her weight. Rumors have swirled in the years since that this was at least partially because Ball demanded her character be the show’s sole glamorous figure, an idea that plays out in Being the Ricardos in a scene in which Vance and Ball debate whether Ethel can wear a dress that actually suits Vance’s figure.

“We find her essentially in a place of mourning. She’s mourning who she was. She’s mourning who she can no longer be, and this is an attempt to save just an ounce of herself.”

But don’t worry—if you, like many, view Lucy and Ethel as the ideal model of true friendship, Arianda thinks that was part of their real-life story as well.

“I think they were best friends,” says Arianda. “We find them in [the film] at a place where they’re struggling with their friendship. Each one wants to be seen by the other for different reasons. But did they at the end of the day love each other deeply? Absolutely.”

For Simmons, he found he had an easy way in to understanding William Frawley, whose friends called him Bill. “For me to play a somewhat cranky, cantankerous, 60-something, old, bald, white guy character actor was not a gigantic stretch,” jokes Simmons.

Simmons and Frawley also shared remarkably similar career trajectories. By the time he was cast in I Love Lucy, Frawley was best known as a performer from vaudeville days, introducing such Tin Pan Alley standards as “My Melancholy Baby” and “Carolina in the Morning,” while also acting on Broadway in a string of plays in the ‘20s and ‘30s, most notably Ben Hecht and Charles MacArthur’s Twentieth Century.

Simmons got his start on Broadway in such shows as Guys and Dolls and Laughter on the 23rd Floor before becoming primarily a film and TV actor. “I just did the math and it’s been 26 years since the last time I was actually in a Playbill magazine at a Broadway theatre,” Simmons shares.

Ultimately, it was the differences between the two that informed how Simmons attacked the role. “He missed a lot in his life. He had an early marriage that ended badly, and he never really found that in his life after that. He did have his love of the work, whether it was vaudeville or Broadway or tiny little supporting parts in movies that gradually got to be more significant, and then obviously culminating in this iconic character in arguably the most iconic television program in the history of American television.”

Arianda and Simmons’ stage backgrounds also let them bring some authenticity to the portions of Being the Ricardos that recreate an episode’s filming. Ball, who viewed a live audience as vital to performing good comedy, insisted that episodes of I Love Lucy be filmed largely as if they were live stage plays, letting the studio audience see the entire episode chronologically and rarely, if ever, going back for another take.

“It does have a very theatrical sense to it,” says Simmons. “You see us backstage, you see us going out in the alley before the show, you see us wishing each other a good show. It is very much like theatre.”

For Arianda, it also informed how the characters would deal with their off-screen drama, all the while knowing that no matter what else happened, an audience would be in the studio to watch their performance Friday night.

“When you work on stage, that is your day. You wake up, you have your coffee, but you know that come eight o’clock the curtain is going up, so you have to be very careful in the way you navigate your day because you have to come 100% with a clean sheet of paper, so to speak, so that somebody else can take over for a few hours. In and of itself, that’s a very high stake.”

Being the Ricardos is now streaming on Prime Video.