The one demand that Gwyneth Paltrow made as a child that surprised her mother.

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Amy Odell's favourite part of writing biographies is starting with a blank page. Going back to square one, with a public figure so well known they're household names — and teasing out the truth.

This proved especially true of her latest release, Gwyneth: The Biography, a book that took Odell three years to research and write, with more than 220 interviews conducted with people who know Paltrow.

The subject, as the name suggests, is Gwyneth Paltrow the Oscar-winning actress and business woman, who rose to fame in the 1990s.

"I thought she would be a good subject because she's been in the public eye for more than 30 years. She's been written about a lot," Odell told Mamamia, explaining this is an "unauthorised" biography.

"It seems countless profiles have been published about her, but I learned doing my research that those profiles barely scratch the surface of who she really is. I thought there was an opportunity to pull back the curtain on what makes her so fascinating and also so polarising."

WATCH: Amy Odell shares some of her favourite Gwyneth Paltrow stories from her research. Post continues after video.

Paltrow was quite literally born into Hollywood. As the daughter of filmmaker Bruce Paltrow and actress Blythe Danner, she established herself as a leading actress before transforming the modern wellness and lifestyle space with the creation of Goop.

One of Odell's favourite discoveries about Paltrow was a story about her childhood years.

"When she was travelling with her parents, because she had this bicoastal childhood going between Los Angeles and New York, she would fly first-class with her father, Bruce, because he liked the high life. He had expensive taste and wore expensive clothing. Blythe was more modest and she would fly coach, with Gwyneth and her brother Jake," she explained.

"Gwyneth, apparently on a flight with her mother, said, 'you mean we're not flying first class, we're flying no class?'

"I love the details."

Blythe Danner, Gwyneth Paltrow, Bruce Paltrow and Jake Paltrow at the "The Prince of Tides" premier on December 11, 1991. Image: Getty.

As Odell sat and wrote, she began to decode the enigma of Paltrow; a figure simultaneously adored and hated, who courts controversy and cultural influence.

"It was so fascinating to hear about how she got her start, how she became who she is thanks to her parents and her upbringing. How those experiences shaped her life and how fame can change a person and how being a celebrity can be a business asset but also stand in the way," Odell said.

"A lot of us probably feel like we know her, because we have seen her so much, we've read so much about her."

So who is Gwyneth Paltrow? Really?

If there's one thing people get wrong about Paltrow, it's just how involved she is with her business, Goop, according to Odell.

The brand was founded in 2008 as a weekly newsletter, with it later expanding into a lifestyle e-commerce empire, selling everything from skincare to wellness products (and of course, "that" vagina candle).

LISTEN: The wild history of Gwyneth Paltrow's vagina candle. Post continues below.

"She basically shaped the modern wellness industry," Odell said. "Goop really provided a template for other brands to copy.

"One, Gwyneth was early to give wellness a rhetoric and a language, so talking about toxins and how we should get those out of our lives with 'clean living,' 'cleaning eating,' 'cleaning beauty.'"

The brand is now thought to be worth around $250 million (USD), according to The New York Times and Cosmopolitan, with the global wellness industry currently valued at $6.3 trillion.

"It was interesting to me to hear about how, when she's running her business, she's really the CEO," Odell said. "This is not a part-time job for her. She really is the CEO, she really runs the business and that's unusual for a celebrity brand."

Uncovering this was a surprise to Odell, who mused Paltrow's acting experience has partly aided her business acumen.

Gwyneth Paltrow founded Goop in 2008. It's now estimated to be worth $250 million (USD). Image: Getty.

"People said she could be 'cold', she could be 'icy'. Some people compared her to Anna Wintour, because they said, 'you know what? She's really like any busy Editor-In-Chief. That said, she can really turn on the charisma and the charm when she needs to," she said.

"For example, when she's pitching investors, she can remember what to say in those presentations and deliver them perfectly like she is reading lines. So her acting experience was a real business asset and I hadn't thought about that before."

Through her interviews, Odell discovered Paltrow has a "perfectionist," ambitious nature, and can go "hot and cold" on people.

"She has downplayed her ambition over the years, maybe because the public doesn't always look fondly on ambitious women," the author explained. "With Goop she wanted to do it all well and do it all perfectly.

"Everything she does, to her credit, she wants to do it really well. She's a perfectionist, and she has really high standards for her team.

"I would describe the dynamic at Goop as this; she has favourites, they can change and when executives are privy to her charisma and, in her favour they feel great, but then when she takes it away, they can get very stressed out.

"I was surprised to hear that she would mime like making a barf face, that happened several times in the book. One at a party and also people saw her do it at the office, like when someone turns around to mime throwing up."

Another fact people under-estimate when it comes to Paltrow is her intelligence.

Paltrow allegedly has a "perfectionist," ambitious nature, and can go "hot and cold" on people. Image: Getty.

"People said she's good with words when she edits stories, she is good with copy. And she had veteran publishing employees in there telling me this," Odell said. "She is really good with language. She also started speaking Spanish perfectly when she was a teenager."

This is partly, according to Odell, what led to the breakdown in her relationship with Brad Pitt, whom she dated from 1994 to 1997 after meeting on the set of the film Se7en.

"People have been shocked about her relationship with Brad Pitt and how she felt like she was smarter than him, I think," Odell said, explaining Paltrow's recent foray as Astronomer's "temporary spokesperson" after the Coldplay affair is evidence of her business smarts.

"She knows how to create a viral moment, and she's not afraid of controversy. As I show in the book, she tries to lean into controversy and create viral moments that way. There's been so many for Goop."

Brad Pitt and Gwyneth Paltrow got engaged in 1996, but split in 1997. Image: Getty.

Indeed, of controversies, there have been — a few.

These include infamously recommending vaginal steaming (a treatment not advised by medical experts), making various statements such as, "I can't pretend to be somebody who makes $25000 a year," "I'd rather smoke crack than eat cheese from a can," and telling E! about how being an actress was much harder than having a 9-5 "office job", because she has to work long hours and be away from her kids.

"There has been a lot of analysis over the years about why she is polarising and why her comments are so triggering to people," Odell said.

"I think what she tries to do quite often, is try and understand 'normal' people and get on their level. I think quite often she is not wrong about what she says, but the way it comes out.

"I think it just reveals the distance between her and everyone else, because she has not had an average life in any sort of way.

"She's grown up around movie stars. Steven Speilberg is her godfather. She's been around wealthy people and taste-makers and the glitterati; that's been her milieu her whole life."

Gwyneth: The Biography by Amy Odell is available in Australia from August 5.

Image: Getty.