It was the end of World War II, the American military had entered Paris, and soldiers lined up in droves outside one Paris store, hoping to get their hands on the ultimate luxury product: Chanel No. 5.

It's been the bestselling perfume in the world for the last 90 years, says Tilar Mazzeo, author of The Secret of Chanel No. 5: The Intimate History of the World's Most Famous Perfume. And, she says, it took much more than marketing to get it to the top.

"It turns out that, Chanel No. 5... is an amazing accomplishment in perfume," Mazzeo adds. In the 1910s and 20s, perfumers were just starting to introduce synthetic scent compounds – and one synthetic in particular, an aldehyde, was used in Chanel No. 5 to "represent a bouquet of flowers that does not really exist in the world."

Of course, the woman behind the iconic brand, Coco Chanel, was full of contradictions – and beneath the veil of success was a darker side.

"She had begun her career in what the French would call the demimonde – the shadowy half world of mistresses. She was the second mistress of a very rich man is really how she got her start, he helped fund her first business enterprise. That history was always something that she was very sensitive to."

Chanel cooperated with the Nazis during the occupation of France, and a number of her lovers stood very far on the right of the political spectrum.

"There was no question that she was anti-Semitic," says Mazzeo. During WWII, she tried to use the laws of Vichy France to get her company away from her Jewish business partners, who had moved to America.

"When the liberation of Paris happened, she was not among the people who had their heads shaved and swastikas carved on their foreheads, which is what did happen to tens of thousands of women," Mazzeo explains. "She was forced to flee France; the rumor at least, and I think it's probably accurate, is that Winston Churchill, who was her neighbor in the South of France, helped her flee."

Still, despite her checkered past, Chanel did leave a mark on fashion and broader culture, especially for women.

"Women didn't wear pants back then. She was one of the first women to make women wearing pants acceptable. What she wanted was to create a notion of women's sexuality where you could be independent and competent, and at the same time still be a woman and be sexy. She really wanted to redefine the notion of what female sexuality was in terms of fashion," says Mazzeo.