You may not know the names behind the original 1950s Las Vegas lounge act, Louis Prima and Keely Smith, but you’ve definitely heard of a duo they influenced: Sonny and Cher.

Like Keely, Cher sang and played deadpan to Sonny’s goofier persona. Both women have Native American ancestry, were the superior singers in their duos, and went on to eclipse and divorce their partners.

Louis Prima was born into a family of Sicilian immigrants in New Orleans where he idolized Louis Armstrong and the original black jazz makers. He had a gruff-edged voice and a twitchy, high-energy physical style. Over a long career, he performed jazz, swing and big band music. Approaching his 40s, he discovered a young singer, later called Keely Smith, whose voice utterly wowed him. He took this 17-year-old ingénue under his wing, taught her everything she knew, married her and together in 1954 they became the first Las Vegas lounge act.

“Louis and Keely Live at the Sahara” started as a musical revue conceived by actress Vanessa Claire Stewart (then Smith) and actor Jake Broder at LA’s Sacred Fools Theatre, where they won a 2008 Ovation Award. Over several years it evolved into its current form as a musical play with a dramatic arc reflecting the duo’s lives, careers and relationship.

Taylor Hackford, the Academy Award-nominated director (“Ray”), had been a fan of Prima and was a friend of Keely Smith. Alongside veteran music theatre producer Hershey Felder, he helped develop the play first for the Geffen’s smaller theater, later for a successful run in Chicago and now for the Geffen Playhouse main stage.

“I felt that their story fit right into the classic ‘Pygmalion’/’A Star is Born’ genre,” he told me in a phone interview during tech rehearsals. “A veteran star reaching the end of his career finds a young talent who he mentors and marries, then watches as she surpasses his fame. And he can’t take it.”

After Hackford saw the original musical revue, he approached Keely Smith. “She was very candid, very salty and very funny. I told her I was thinking about getting involved with this production and wanted to make it true and not make stuff up. And she very generously sat down with me, went through her feelings and point of view about their relationship.

“The bittersweet quotient is that they broke up but it was clear that Louis was the love of her life. She said ‘I’ve always had a great voice, no one gave me that but God. But in terms of my musicality, and teaching me everything about jazz, music and how to front a band, it all came from Louis. Every time I get onstage to this day, he’s standing next to me.’” (Prima passed away in 1978.)

While they weren’t as famous as the Rat Pack, “Louis and Keely were very influential,” Hackford explained. “Louis didn’t write much, but he did write ‘Sing, Sing, Sing,’ the anthem of the swing era. He worked the American Songbook and he could make a 6-piece combo sound like a 20-instrument orchestra. He had a brilliant ability to arrange and conceive those songs in a way that no one else could.  No one can beat his version of ‘That Old Black Magic.’ He didn’t write it, but he owned it.”

And, says Hackford, “They may not have been big stars, but there was no such thing as a lounge act before Louis and Keely. The headliners would finish up at 12:30 in the morning, come out, gamble a bit then go to bed, so the casino was moribund at night.

“Someone said, ‘What if we put entertainment in middle of the casino?’ Louis had just picked up Keely, and they were given a two-week gig on the floor of the Sahara casino. They were plunked down in the middle of the casino floor on a riser, with two palm trees on either side, and had to compete with the slot machines, dice tables, roulette wheels, card tables and the gamblers.

“They took that, did five shows a night starting at midnight, with the last show at 5 a.m., turned it into a major act and built a career around it. The headliners would come out to watch them and (comedian) Don Rickles, who came to see our show several times, told me he even opened for them at the start of his career.”

Broder was the same age as Stewart when he originated the role of Prima. Now Tony Award-winning actor/singer Anthony Crivello, who performed to critical acclaim in the Chicago production, plays Prima. His Sicilian heritage, and the 23-year age difference between him and Stewart impart a certain resonance: Louis was 23 years older than Keely.

Says Hackford, “From a directing point of view, you want to motivate your actors, but I don’t need to motivate Anthony. For Italians of a certain generation, Louis Prima is as important as Frank Sinatra and Tony understands that. He’s got his uncles, aunts, grandmother, grandfather and parents on his shoulders saying, ‘You better not screw this up!’

“And with Tony and Vanessa, we get that true May-December aspect, one at the back end of his career, the other at the beginning of hers and her personal evolution, which adds a dramatic quotient that’s palpable onstage.”

“Louis and Keely Live at the Sahara” is onstage at The Geffen Playhouse through Jan. 17. Visit www.geffenplayhouse.com for details.

Photo: Vanessa Claire Stewart and Anthony Crivello as Louis and Keely. Photo by Eighty-Eight Entertainment.

Sarah A. Spitz spent her career as a producer at public radio station KCRW-Santa Monica and produced freelance arts reports for NPR. She has also written features and reviews for various print and online publications.