When Barbie dolls were first introduced in 1959, little girls snatched them up in droves. For the first time, midcentury kids could play with a doll that looked like a woman, not a little girl—a doll with a sassy ponytail, heavy eyeliner, a healthy dose of side-eye and a distinctly adult body.

Fans had no way of knowing that Barbie had an even more adult side: She was closely related to a German novelty toy.

Barbie had a sister—Bild-Lilli, a racy doll marketed to men. And though the risqué 1955 doll has largely been overshadowed by the success of the American toy, she plays a part in the origin story of an American icon.

The story of Barbie began with Ruth Handler, an American businesswoman who co-founded the toy company Mattel with her husband, Elliott. As Ruth watched her preteen daughter, Barbara, act out stories with her paper dolls, she wondered why there wasn’t a more grown-up doll for kids who had outgrown baby dolls and bedtime stories. Handler created Barbie with the intention of having a womanly 3-D doll that could be styled and dressed up like a paper doll.

But when Handler shared her idea with her husband, Elliot didn't get it. He said no mother would want to buy her child a doll in the shape of a woman. His colleagues agreed. “They were comfortable with toy guns and rockets, musical instruments and pop-up toys, but the doll Ruth described defied their imagination,” writes business historian Robin Gerber.

The Mattel staff told Ruth to forget it—her ideal doll would be controversial, unpopular and too hard to produce. (Today, Barbies are banned in some countries including Iran in what government officials say is an attempt to protect the public from Western influences, which they see as responsible for eroding Islamic values.)

Then Handler and her family took a trip to Switzerland—and met the doll that would change their lives forever. Her name was Bild-Lilli—but she wasn’t for kids. Rather, the doll was modeled after a popular comic character from the German-language tabloid Bild. Lilli was a gold-digging sex symbol created by Reinhard Beuthein. Single and more than ready to mingle, Lilli was drawn with a comically over-the-top body that featured a disproportionately large bust. The character was often portrayed in scanty clothing and gave snappy comebacks to slobbering men.

In one strip, Lilli is being pursued by two businessmen on the street. “I’m going to have to ask at least one of you to stop following me,” she says slyly. In another strip, she is portrayed in a scanty tennis outfit that wind blows up to reveal her underwear. “I never used to be interested in sports, but the newest tennis fashions at Wimbledon have given me a new perspective…” she smiles.

Lilli was supposed to be a one-off comic, but she was so popular that she became a fixture in the paper. In 1955, Lilli dolls made their way onto the shelves of tobacco shops and adult stores in the German-speaking world. They became a beloved gag gift popular among men.

Handler was enchanted by Lilli’s womanly shape—but not because of her appeal to men. Here was the kind of doll she had envisioned. Handler admired Lilli’s different costumes and her 11.5-inch form. The doll proved that her dream was possible, after all. “Handler decided to reinvent this pornographic caricature as the all-American girl,” writes art historian Carol Ockman.

Soon, Lilli was on her way to Japan with a Mattel researcher who had been tasked with finding a manufacturer. As Gerber notes, the doll’s over-the-top body and exaggerated face were softened by Mattel’s design team. But the Barbie doll that resulted still looked a lot like Lilli.

When the doll debuted in 1959, she was billed as a fashion model, and she was an instant hit. Handler’s gamble worked—there was simply nothing like Barbie out there. But to some, including Lilli’s creator, Barbie looked an awful lot like Lilli. “I was outraged when I saw this doll,” recalled Rolf Hausser, whose toy company created and sold the Lilli doll. “This was my Lilli with a different name. What had these people done? Had they stolen my doll? I didn’t know what happened.”

Greiner & Hausser struck a licensing deal with a Mattel rival, Louis Marx, who began using the Lilli head molds to create “Miss Seventeen,” a less successful Barbie competitor. Then, Marx and Hausser sued Mattel for infringing on Lilli. But the lawsuit was unsuccessful, and Hausser sold the copyright and patents to Lilli to Mattel in 1964 for a small sum. Hausser’s company soon went bankrupt.

But that wasn’t the last time Lilli would rear her ponytailed head: In 2001, Greiner & Hausser filed another lawsuit against Mattel claiming it had been pressured into the settlement and seeking royalties on every Barbie sold since 1964. The case was eventually dismissed.

So was Barbie really a Lilli knockoff? “Well, you might call it that,” Ruth Handler’s husband, Elliot, told biographer Jerry Oppenheimer in 2008. “Ruth wanted to adopt the same body as the Lilli doll with some modifications. Changes were made, and improvements were made. Ruth wanted her own look.”

Today, though, Mattel downplays the connection. “Ruth was inspired by watching her daughter play with paper dolls. The Bild Lilli doll proved it was possible to manufacture an 11 ½ inch doll,” a Mattel spokesperson told HISTORY. Today, there are over 100 Barbie dolls sold every minute—and her long-forgotten, more risqué sister has become a historical footnote.