'Mamma Mia!' turns 15: An inside look at how an A-list cast came together with Greek locals to make a beloved ABBA musical

• "Mamma Mia!" premiered in theaters in July 2008, exactly 15 years ago.
• The feature film stars Meryl Streep, Amanda Seyfried, Pierce Brosnan, Christine Baranski, and more.

At its core, "Mamma Mia!" is a simple story about a bride-to-be in search of her father, but it's one with staying power. Fifteen years have passed since the blockbuster's release, and miraculously, it's still everywhere.

Millions of TikTok videos are set to ABBA soundbites. People pay 100 pounds to attend a "Mamma Mia!"-themed dinner show in London. And every couple of months, grainy photos of cast members Christine Baranski, Meryl Streep, and Colin Firth letting loose at a wrap party make their rounds online, giving people retroactive FOMO.

In honor of the movie's 15-year anniversary this July, Insider spoke with members of the cast and crew about their experience bringing the story to the screen, their time shooting in Greece, and their perspectives on the movie's legacy.

The idea for 'Mamma Mia!' came to Catherine Johnson during an interview to write the stage musical

When producer Judy Craymer was looking for a writer to pen a jukebox ABBA stage musical in the late '90s, Catherine Johnson knew she wasn't the obvious choice for collaborator.

The playwright's previous work had mostly been in fringe theater and TV ("Casualty," "Bands of Gold," and "Byker Grove"), and she wasn't particularly well-versed in the Swedish group's discography.

Fortunately, a concept for the musical came to Johnson "out of nowhere" during her interview with Craymer, the writer told Insider. "The idea of the mom, the daughter, and the three possible dads just descended on me, and it gripped me with an intensity," she said.

The musical, which Craymer worked on with ABBA members Benny Andersson and Bjorn Ulvaeus, premiered in London's West End in 1999, making its Broadway debut two years later in 2001 and running until 2015.

The production has been nominated for accolades ranging from Olivier Awards to Tony Awards — and the US show won the Touring Broadway Award for best long-running musical in 2005. The "Mamma Mia!" craze only grew once the film adaptation premiered in 2008.

When it was time to cast the film, the talent had to be able to dance, act, and sing (or, at the very least, hold a tune)

There was widespread interest in bringing the stage musical to the screen, and Universal Pictures ultimately bought the film rights, with Craymer, Johnson, Andersson, Ulvaeus, director Phyllida Lloyd, and choreographer Anthony Van Laast on board for the adaptation.

The pressure was on to cast the ensemble, and Craymer already had her sights set on the ultimate Donna Sheridan: Meryl Streep. Fortunately, it seemed like Streep was already a fan of the musical.

Priscilla John, a "Mamma Mia!" casting director, told Insider that the Oscar winner had written a note to Craymer after seeing the Broadway musical in the aftermath of the 9/11 terrorist attacks, telling her that "Mamma Mia!" made her and her family laugh and smile for the first time in months.

With Streep on board, the casting directors had to flesh out the ensemble, a tricky feat considering the project wasn't just about screen presence.

"We knew that they could act, but could they sing?" John said. According to Orla Maxwell, a "Mamma Mia!" casting associate, Firth showed up with a guitar during auditions before landing his role as Harry Bright, one of Donna's former flames.

Pierce Brosnan — who took on the role of Sam Carmichael, one of Sophie's potential fathers and Donna's love interest — drew some criticism for his vocal performance in the film, snagging a Razzie Award for worst supporting actor in 2009.

But casting someone with perfect pitch wasn't the team's priority.

"They all loved him because he didn't sing very well. He sang like all our dads, and that was the criteria really. Everybody was free to sing, and they didn't have to be trained singers," John said. "They just needed to sing in key, as if they were having a ball."

She said the team "fell in love" with Amanda Seyfried and decided the American actor would be a perfect fit for Sophie Sheridan, the young bride in search of her father.

"She looked like Meryl, and she was the sweetest thing," John told Insider. "She was very naive in a way. She was beautiful, happy, naive, and sweet."

The role of Sky Rymand, Sophie's fiancé, went to Brit Dominic Cooper. Though John said Seyfried and Cooper didn't do chemistry reads, both the UK and American casting professionals made a judgment call to pair them together, one that paid off.

Cast members had to make it through several workshops and auditions before securing their roles. Philip Michael told Insider he went through a "gruesome seven auditions" before he learned he'd play Pepper, Sky's best friend and a bartender on the Greek island.

"Everybody had to go and do these workshops and show that you can learn some steps very quickly and sing at the same time," Mia Soteriou, an actor who played a supporting character named Arina, told Insider.

Van Laast, who choreographed the stage musical and the film, said he was looking for talent that could move well, but they also needed to have personality. As he got to know the actors better, he adapted the movements to fit their personalities, telling Insider that high-caliber performers "always bring something to it that you wouldn't necessarily have imagined."

Once the cast was all set, Johnson made some changes to the script to make sure it served each actor. Spending time around the cast and getting to know them gave her a better idea of how far they would go in their performances. For instance, she wrote a scene in which Bill Anderson — one of Donna's former beaus, played by Stellan Skarsgård — is in a towel and flaunts his bare butt.

"I thought, 'He won't mind getting naked.' And I felt quite confident that if I put that in for Bill, Stellan would be up for it," Johnson said, adding, "Spending time with them very much informed what I was writing."

As for Van Laast, he used the free days during shooting to venture to mainland Greece with other crew members to cast locals. The choreographer said many of them didn't speak English, so the crew taught them the lyrics to songs like "Dancing Queen" phonetically.

Casting "all the old grannies" who appear in the film ended up being one of John's favorite experiences during production.

The team used a DVD of "ABBA Gold" to teach them to dance, John recalled. "It was a joy to see them coming down through the hillside, with the sticks and the washing and having a great time," she told Insider.

While shooting the film in Greece and England, the cast members improvised some scenes on the fly

Although the entire film takes place on a fictional Greek island called Kalokairi, the group only spent three weeks on Skopelos, an island in the Aegean Sea, during production. Many scenes set in Kalokairi were filmed at Pinewood Studios in England.

Thanks to all of Johnson and Lloyd's groundwork, there weren't many rewrites on set. The "Money Money Money" musical number, in which Donna daydreams about a luxurious, opulent life far from her crumbling Greek inn, needed the most attention.

Johnson initially conceived it as a Busby Berkeley-inspired idea with synchronized divers. When they realized it wasn't going to work, they filmed the scene on a yacht instead.

Many of the beach scenes were also filmed in Greece, including the iconic "Lay All Your Love On Me" number between Sophie and Sky (and a pack of toned, bronzed men who emerge out of the waves in tiny trunks). Van Laast had included the flipper-footed dancers in the stage musical's choreography, but he upped the ante for the screen.

"When they all came down the jetty doing that running, I thought it looked really great," he told Insider. "The day we were filming, the weather was terrible. Everyone was frightened that the jetty might actually fall to pieces. It had been built for the film. We had divers underwater to make sure that if it went down, everybody would be safe."

Michael, a fairly green actor at the time, also had to put his trust in the "Mamma Mia!" vision, as he had to anchor the "Does Your Mother Know" scene with acclaimed Broadway star Christine Baranski.

He'd spent 11 weeks in rehearsals mastering his steps, only to learn that the majority of this specific scene would be improvised around Baranski. Despite knowing the script front and back and appreciating the "freedom of creativity," Michael said, he was a "nervous wreck" on filming day.

"That was the scariest day of my life," he told Insider. "I'm super nervous, and then Phyllida comes in and says, 'OK, show me what you got,' and then goes off behind the camera. The choreographer comes in and says, 'Don't worry about it, just improvise around her.'"

Michael followed Baranski's lead, explaining that he was "learning everything as we went along."

When the cast wasn't shooting, they went jet skiing, mingled, and dined at local spots. The island was small, so they saw pretty much everything in the span of two or so days, Michael told Insider.

Despite those viral wrap-party pictures, the actor said activities tended to be fairly low-key because of the intense filming schedule (they had to be up and ready by 5 a.m.).

Over a decade since the movie's premiere, 'Mamma Mia!' remains a feel-good sensation

Following the stage musical's success, people expected the "Mamma Mia!" movie to be big. Still, many of the cast and crew involved in the film were taken aback by the box-office darling's success.

The film garnered Grammy, BAFTA, and Golden Globe nominations. It also prompted a 2018 sequel, "Mamma Mia! Here We Go Again" and a talent show from ITV called "Mamma Mia! I Have a Dream," which doesn't have a confirmed release date at the time of publication.

Fifteen years later, audiences are still enjoying the timeless film. As Van Laast said, "There's a basic storytelling art, which Catherine Johnson found with Judy. The very simple story of a girl looking for a dad resonates with a lot of people."

For others, the movie's aqua waters and group dance numbers are a boost of serotonin. "What more could I wish for than to have been part of something that people turn to when they want to feel good?" Johnson said. "If that's the legacy, let it be that it's a feel-good movie."

And of course, there would be no "Mamma Mia!" without ABBA. "That music is also such a collective experience," Maxwell told Insider. "This story is universal, but the music is the glue that everyone can relate to, from granny to grandchild."

Representatives for Streep and Brosnan did not immediately respond to Insider's requests for comment.