Some of your favorite Muppets characters have surprisingly emotional backstories.

The Muppets have been a cultural institution for more than 40 years. But their creators had never sat down to talk about their work.

Since "The Muppet Show" debuted in the 1970s, there have been eight feature films, reboots of the show, and a number of specials. Their legacy is undeniable, with each generation finding inspiration and meaning from the puppet characters first created by Jim Henson .

But in the new documentary " Muppet Guys Talking ," Frank Oz (creator of Miss Piggy, Fozzie the Bear, Animal, and Sam Eagle) reveals that in all those years he and his fellow Muppet performers had never discussed where it all came from.

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"You have fellow employees, how often do you get together and talk about work?" Oz says.

Oz's wife Victoria Labalme overheard her husband sharing stories about his past and came up with the idea for the film, saying it would be a rare chance to give fans of the Muppets a look behind the curtain — but also an opportunity to get these creative genius minds together in one room.

"There was no agenda," Oz says. "We just showed up and started talking."

Instead of going through major distributors or movie theaters, they decided to release the documentary independently through a website they created themselves. "It gave us an opportunity to build a community," Labalme says.

What ensued was an intimate and touching chat between five close friends who were often as surprised as the film's viewers when they learned in real time where so much of the Muppet magic originated.

The Muppet characters' origin stories are surprisingly complex.

The opening of the documentary reveals that, at the height of the show's popularity in 1978, an estimated 235 million people were tuning in each week in 102 counties to experience the adventures of Kermit, Miss Piggy, and their merry band. More than half of those viewers were adults.

Part of why the show resonated so much with adults, as well as kids, was because of the creators' approach. They were focused on telling great stories first. And great stories need great characters that mirror humanity back at the audience.

Oz recognizes that humanity in the characters he's created. He's said that Miss Piggy may be the most "three-dimensional" of his Muppet characters, while Fozzie the Bear is surprisingly the most tragic.

Photo by Matt Winkelmeyer/Getty Images.

Miss Piggy is a complicated character, full of seeming contradictions, impulses, and conflicts. Oz initially imagined her as "a truck driver who wanted to be a woman," before developing a more complex biography of a girl whose father died and whose mother neglected her. Piggy was forced to enter beauty pageants from a young age and is continually seeking stardom and fame to compensate for her insecurities, which are often funneled into her relationship with Kermit.

Meanwhile, Fozzie is the aspiring comedian who left home to pursue his dream but never lands a joke. "All of the characters have a key to the playhouse, except for Fozzie," he says. These characters' histories are as complex as Oz himself. "I was a very shy person. I was internal. To a great degree I still am introverted," he says. "The puppets protected me from being rejected."

Photo by Antony Jones/Getty Images.

Audiences responded to the humanity and vulnerability in these characters — and loved it.

It wasn't just Piggy and Fozzie either. In the film, the other performers (Fran Brill, Jerry Nelson, Dave Goelz, and Bill Barretta) revealed the inspirations of their famous characters, where are deeply personal for all of them. Their characters were based on family members or transforming personal "flaws" into something more "lovable" for a broader audience.

The humanity of these characters resonated with audiences in a meaningful way and it was moving for the creators. All the Muppet performers agreed that there was something special about seeing people almost instantly forget about the person involved and start talking directly to a puppet as if it were a living, breathing, independent being.

They always sought to entertain and tell the best stories they could, but they quickly realized that disappearing into these characters gave millions of viewers the chance to connect with something special that was intrinsically a piece of themselves. "You don't have the limitation of your own body you can become any character," Oz says. "You can become any character you can put on."

That magical connection between creator, puppet, and audience is as special and unique as each of the Muppet characters — and the people behind them. And it's what sustained the legacy for all these years.

[rebelmouse-image 19478353 dam="1" original_size="1024x683" caption=" Photo by Jeff Christiansen/Flickr " expand=1] Photo by Jeff Christiansen/Flickr