Washington - When she was about 14, Hillary Clinton says, she wrote to Nasa volunteering for astronaut training.Nasa's reply was simple and definitive: No girls."It was the first time I had hit an obstacle I couldn't overcome with hard work and determination and I was outraged," she would write in her book, "Living History."More than a half-century later, and after much hard work, much determination and most of all, many, many obstacles - some undeniably of her own making - Clinton is no closer to actual space travel. She may have to settle for becoming the first female leader of the free world.Clinton and her running mate, Senator Tim Kaine will debut as a presidential ticket in the crucial battleground state of Florida as they head toward next week's Democratic Party convention.They are set to appear at Miami's Florida International University on Saturday.Glass ceilingClinton's journey...more than three decades in the public eye and counting...has been unlike any seen in American politics: a story of great promise, excruciating setbacks, bitter scandal, stunning comebacks and especially re-invention. Think about it: Is any woman more recognisable on a global scale than Hillary Clinton? If Barack Obama was the presidential candidate who seemed to come out of nowhere, Clinton's the candidate who seemed to come out of everywhere.Americans first knew her as a governor's wife and working mother in Arkansas, then as the nation's first lady - famously claiming an office in the West Wing of the White House, not the East, as half of husband Bill Clinton's "Buy one, get one free" bargain. Touched by scandal from Whitewater to Monica Lewinsky - but also carving out her own political identity - she emerged to become a hard-working senator, the first first lady to gain elected office. We knew her as the presidential candidate who suffered a stinging defeat to Obama in 2008, but proudly claimed "18 million cracks" in the glass ceiling.Then she re-invented herself again, becoming Obama's secretary of state, traveling almost a million miles to 112 countries. Finally, after much speculation, she announced her second run for the presidency.We knew her so well by then.Or not. Who WAS Hillary Clinton, and why, if we'd been watching her for so long, did we feel like we didn't know her?At least, that's the persistent narrative. Perhaps it's a question of layers. She's had so many different roles, of course we've seen different facets of her. But there's also a sense of impenetrability, exacerbated by her penchant for secrecy - a characteristic that has led to her greatest vulnerability in this election: the email scandal over her use of a private server.For the last 14 years, and 20 overall, Americans polled by Gallup have named Clinton their most admired woman in the world. But consider some other titles attached to her over the years: Lady Macbeth. Washington insider. Robotic. Wildly ambitious. Congenital liar. (Or Donald Trump's current favourite, "Crooked Hillary.")But also: Feminist heroine. Glass-ceiling breaker. The most prepared in the room. The most qualified presidential candidate ever. Loyal friend. Witty companion. Mom. Grandma.Showing ambition"It's an amazing life," says biographer Carl Bernstein, who wrote a 600-page book on her and says he still struggles to define her. "You could not make any of this stuff up."There have been polarising figures in politics before, but it's hard to imagine any have been called as many things — wildly divergent things — as she. Does everyone simply have their own version of Hillary Clinton?Saturday Night Live has been turning out versions for a good 25 years. Each actress spoofing Clinton - there have been nine, including Miley Cyrus rapping in a bandeau - has put her spin on the part. But there's been one constant: ambition, pure and unadulterated.Comedy aside, the ambition tag has dogged Clinton, 68, throughout her career, as if it were a bad quality rather than a necessity in high-stakes politics. The satirical website The Onion captured the irony in a 2006 headline: "Hillary Clinton Is Too Ambitious To Be The First Female President."That gets a knowing laugh from Melanne Verveer, Clinton's chief of staff from her first lady years."If a guy is described as ambitious, it's a noble attribute - he wants to put himself ahead," says Verveer. "But if a woman is ambitious, it's not an attribute, it's a negative, a pejorative. It's not proper somehow."Former Republican Patricia Schroeder thinks the ambition factor is - unfairly - key to Clinton's challenges connecting with the electorate."We still don't like a woman who is showing ambition, especially for that level of a job," says Schroeder, who famously explored her own presidential candidacy decades ago. "It's: 'I'd like her if she weren't so damned ambitious. How come she wants all that power?' "At her college graduation in 1969, Hillary Rodham was already blazing a trail: The senior from Park Ridge, Illinois, was the first student chosen to address a Wellesley commencement. She delighted many classmates when she delivered an on-the-spot rebuke to the previous speaker, a US senator whose comments the grads found condescending to women. At Yale Law School, where she met Bill Clinton, she developed a keen interest in children's rights, which she pursued in post-graduate work.It's been a particular frustration to Clinton's campaign that young Democrats haven't responded more enthusiastically, with many attracted to the populist message of Bernie Sanders (six years her senior). There's a sense that millennials are too young to remember her efforts on behalf of social justice, particularly for women and girls on a global scale.Never understood "Young people today want to be part of something bigger ... but they don't understand how much she shares those aspirations of theirs," Verveer says.A key moment in Clinton's political journey — and a defining personal moment — came in 1995, when as first lady she spoke at a UN Congress on women in Beijing, declaring, "Human rights are women's rights and women's rights are human rights."It was a time when Clinton was searching for a new identity, having failed to reform health care back home. But even she had no idea the impact those simple words would have."It not only gave her an instant sense of the world looking at her differently, but she was also seeing the role she could play — in ways perhaps she had never understood before," Verveer says. "It has remained with her ever since."Part of the narrative on Clinton has been her trouble connecting to the public. "I am not a natural politician, in case you haven't noticed," she said recently, "like my husband or President Obama."In a February Gallup poll, the most common responses Americans gave when asked what came to mind about Clinton were "dishonest" and "dislike her." (For Sanders, they were "socialist" and "old.")Fair or not, it's a theme woven into the Clinton story — both Clintons — from the White House scandals to the email story.