It made sense that Buzz Aldrin, a man who has walked on the moon and lived without gravity, was in Rio to watch a teenage compatriot defy the earth's forces like no other athlete in history.

The former astronaut cheered as the United States won the women's gymnastics team title on Tuesday and saluted the special quintet, one of whom was the extraordinary Simone Biles.

Biles, the innovator, the ground-breaker, is a gymnast who comes along every other generation or so - a 19-year-old hailed as the most talented anyone has seen. She is already a superstar of her sport and, by the time the Olympic flame is extinguished, is likely to orbit the same space as the planet's most recognisable stars.

This 4ft 8in gymnast from Texas, placed into foster care because of her mother's struggles with drugs and alcohol and adopted when she was five by her maternal grandfather and his wife, has already won two Olympic golds at her debut Games.

She could win five. She is expected to win five. She is almost untouchable.

What makes Biles so good?

Prior to Rio, Biles had already won a glut of major medals

It is the end of June, at the American national championships in St Louis, and the Olympics are fewer than two months away.

Biles is in the middle of her floor routine. Watching on is 2008 Olympic all-around silver medallist Shawn Johnson. The reigning champion spots Johnson in the crowd, cheekily winks at her and flashes a smile, before continuing to perform vertigo-inducing somersaults.

No-one else would have the chutzpah. No-one else looks like they're having so much fun.

The athlete herself says it is her ability to enjoy the spotlight which sets her apart. "It's how it works best for me and how I get success out there," she says.

But cheer and calmness are not the only attributes that separate the ebullient American from the rest. It has been three years since Biles, her sport's first black female world champion, entered an all-around competition and did not win.

No female gymnast has ever had her power, reached such soaring heights, been so consistent and performed jaw-dropping routines with such joy. "I would make the case that she's the best athlete in Rio," says ESPN's TJ Quinn.

The differences between the three-time world champion and the others are not subtle. She is faster, stronger - her powerful run allows the teenager to include more elements in her routine than competitors who have to go further before they can start tumbling.

On the floor, the girl described as having legs made by Nasa can leap a foot or two higher than her rivals. Her coach Aimee Boorman has said her pupil has exceptional "air sense", the innate ability to know where she is in mid-air.

Biles is also bolder and more consistent, too. Small and light, her compact body is also perfect for her sport.

"She's certainly doing the most difficult work we've ever seen," says Christine Still, a gymnastics coach and member of BBC Sport's commentary team. "In terms of performance and her ability to perform again and again, she's the best I've ever seen."

As a child, Biles would watch older girls and copy them with ease. According to her coach, she will learn a new skill in three days, while most gymnasts take months or years to master a move.

Quinn asks: "How many sports can she enter? I wouldn't be surprised if she could dunk a basketball."

How big a star is she already?

Biles has been turned into an emoji

At this year's Pacific Rim Gymnastics Championships, Biles decided to skip the second day of competition and watched on from a hospitality box, but a group of young girls saw their diminutive hero. Biles, forced to think as adroitly as she usually moves, had to call security to stop the fans from climbing into the suite.

In March, Biles admitted on The Ellen DeGeneres Show she had a crush on Hollywood actor Zac Efron. If the pair were to meet - they have been tweeting each other - they could discuss tales of a life lived with devoted fans.

If more evidence of her celebrity on home soil was needed, NBC's footage of that St Louis routine - where Biles winked at Johnson - was reportedly viewed more than 11 million times on the internet in just the first few days.

And it is no surprise to learn that the girl with the megawatt smile is the most searched female gymnast on Google and has her own emojis, with an app launched before the Olympics called Simoji.

Her profile is increasing around the world, too. During Tuesday's team final, the five countries where her name was Googled most were USA, Republic of Ireland, Canada, Spain and New Zealand.

Following her magnificent all-around performance on Thursday, she was trending on Twitter - generating two-and-a-half times more tweets than anything, or anyone, else at the time.

"Most Americans love her and why not?" says Louis Moore, associate professor of African American, sports and gender history at Grand Valley State University. "She's successful, amazing to watch, and her success helps push narratives about hard work and democracy. She's primetime TV.

"Given her background and sport, there's not another athlete like her historically. There's been anticipation for this moment for quite some time."

Biles was on the cover of Sports Illustrated's Olympic special, alongside the likes of Michael Phelps, Kevin Durant, Alex Morgan and Katie Ledecky

What is 'The Biles'

Biles flips and spins on the four-inch-wide balance beam as if she were on a pavement. On the vault, she does the Amanar - one of the hardest moves performed by women - and no-one can match her height, execution and consistency.

But it is on the floor where she truly astonishes, dazzling spectators with 'The Biles' - her signature move - which is incorporated into the hardest floor routine in history.

Almost as exhausting to describe as it is to perform, it is a double backward somersault with the body fully extended, followed by a half-twist and a blind landing. At the peak of the move, she clears nearly twice her height, the equivalent of tumbling over a football goalpost.

Until Biles did so in 2013, no-one had ever tried the move in competition.

"I love it," says Beth Tweddle, the British London 2012 uneven bars bronze medallist. "She's got that personality, she really showcases gymnastics."

'Just give Simone Biles the Gold Medal' was a recent headline in The Wall Street Journal as the American newspaper described her as the "heaviest favourite in the entire Olympics" for all-around gold.

There was logic behind the bombast - and they were proved right as she sparkled on the grandest stage on Thursday to become only the second woman in history to hold both the world and Olympic all-around titles.

Biles performs routines which are so much more difficult than her rivals that others would have to be near flawless and hope for Biles to falter badly to have a chance of catching her. That has yet to happen in Rio.

This special talent - called "a once-in-a-thousand-year athlete" by William Sands, a former research director for USA Gymnastics - is capable of more.

Training videos show Biles pulling off gravity-defying tricks on a different level to what is seen from her in competition. "She's obviously competing at a level below what she's training," says Tweddle. "She makes it look very easy."

Former 200m and 400m Olympic champion Michael Johnson once said Usain Bolt could run quicker were he to strengthen his core muscles. The Jamaican hasn't heeded Johnson's advice because he doesn't have to - he is already the fastest man in history.

The same applies to Biles - why attempt trickier routines in public when she is already better than the rest by some distance?

She has come up with her own floor move - 'The Biles'

How big could she become?

Four years ago, Biles' fellow American Gabby Douglas arrived in London with no sponsorship - only after becoming the first black woman to win all-around Olympic gold did big businesses chase her.

Biles, owner of more World Championships gold medals than any female gymnast in history, already has a champion's portfolio with 'wholesome brands' such as Nike, Kellogg's and United Airlines firm in their belief that Olympic greatness is a foregone conclusion.

Rick Horrow, visiting sports business expert at Harvard law school, says Biles has the "It factor".

"She has the charisma, the appearance of humility, the looks, the radiance when interviewed to build on that capital," he says.

Her current earnings of $2m (£1.5m) a year, he says, could be a "scratch in the bucket" if she wins five gold medals in Rio and becomes a familiar face outside the gymnastics world - appearing regularly on TV and corporate events. "The kinds of things that celebrities do beyond the sport itself," adds Harrow.

She is not yet a Michael Phelps, the most decorated Olympian in history, but she has strong foundations from which to build.

Impact beyond gymnastics

Biles has admitted she has a crush on actor Zac Efron

"She's the best I've ever seen," says 1984 Olympic all-around champion Mary Lou Retton, while 2008 all-around champion Nastia Liukin is equally lavish in her praise, describing her as "the best gymnast that has ever lived".

But there is more to Biles than gymnastic genius. "Her story is incredibly compelling," says Quinn.

She was adopted by grandfather Ron, an air traffic controller, and his wife Nellie, a former nurse, as her birth-mother, dependent on drugs and alcohol, was unable to care for her eight children.

The girl who accidentally stumbled upon gymnastics when on a field trip as a six-year-old is also a member of the most racially and ethnically diverse group of Olympic gymnasts in the American team's history.

"They are demonstrating there really are no racial boundaries from the standpoint of participation in our sport," said USA gymnastics president Steve Penny.

Of the five women representing the United States, Douglas and Biles are black, Laurie Hernandez is Hispanic with Puerto Rican heritage and Madison Kocian and Aly Raisman, who is Jewish, are both white.

Biles is not the first black American gymnast to compete at the Olympics and she is not the first black woman to win the Olympic all-round gold - her team-mate Douglas did so in 2012.

But US President Barack Obama has spoken this year of his country's deepening sense of alienation and anger, so will Biles' Olympic achievements positively impact an America which is politically and racially divided?

"African Americans, especially young girls, get an opportunity to see themselves in Biles; not so much winning a gold medal, but the adulation and cheers that come with it," says Professor Moore.

"In this society, we don't do a great job of celebrating black women the way we should.

"African Americans also get an opportunity to see a black person succeed in a space that has traditionally been seen as off limits - but we're in the midst of a Black Lives Matter movement for a reason.

"Most African Americans are still fighting for equality, better schools, equal pay, access to jobs - and also an end to abuse from police and the criminal justice system.

"Her success should be celebrated, it's a great story, but we also have to remember that Biles' success won't change the problems most African Americans still face.

"In the end, however, I think her success will inspire others to dream - and everyone will remember this as the Olympics they saw Simone Biles."

Biles with family and friends

Biles relaxing away from gymnastics