Story highlights Sara Blakely is the founder of Spanx, a hosiery company present in 50 countries

Her business idea was sparked in 1998 from "the way her butt looked in white pants"

Blakely was crowned America's youngest self-made female billionaire by Forbes magazine

She attributes her success to extraordinary perseverance, salesmanship and risk-taking

From a woman who sold fax machines door-to-door to being named a billionaire, Sara Blakely's career trajectory has been anything but usual.

No Ivy-League MBA in sight, Blakely has helmed Spanx, a company that produces slimming bodywear -- bras, panties and more -- to a presence in more than 50 countries and an estimated value of over $1 billion, according to Forbes . With product names such as "Bra-lellulah" and headquarters complete with boudoir-like red walls, Blakely's empire is the opposite of corporate. Even the inspiration behind her privately-held company is like no other -- her own rear.

"I just did not like the way it looked in white pants," says Blakely. "That moment inspired Spanx. I had been doing some soul searching and visualization of my life to create a product that I could sell to millions of people."

Spanx revenues for 2011 were estimated at just under $250 million, according to independent research by Forbes Magazine. The magazine also cited that four Wall Street investment banks valued the company at $1 billion.

This year, Spanx expanded into standalone retail stores in the U.S., opening two in November and a third in this month. What started out as a pair of pantyhose with its feet cut out in 1998, has evolved into a diverse business that includes active wear, menswear and swimwear.

In person, Blakely, 41, is attractive, chatty and breaks out into a wide grin frequently. Shunning businesswoman power suits, she's often spotted in a pair of jeans and cotton T-shirt, wearing her hair in hair bands.

Professionally too, Spanx defies the odds.

Where over 50% of American small businesses fail in the first five years, according to figures from the U.S. Small Business Administration, Spanx, now 12, has weathered the economic crisis and Blakely is planning further international expansion. They will begin selling in Italy in early 2013, with plans to target Brazil, France, Eastern Europe, China, India and Russia.

Blakely credits her success to getting comfortable with failure and rejection early. After failing the LSAT law exam, her lifelong dream to be a lawyer was dashed. After a short stint as a ride greeter at Disney World she spent seven years selling fax machines.

She describes her days as a door-to-door salesman as "very difficult, very humbling with lots of tears." Blakely now says she's grateful for the great training she got from "having doors slam in my face."

Blakely launched Spanx with just $5,000 and an unwavering belief the product was exactly what the world needed (she patented it almost immediately). Then, as she faced rejection upon rejection meeting with mill-owners in North Carolina, trying to find someone who would make her girdle, she says her perseverance combined with -- wait for it -- her lack-of-experience, eventually won out.

"I used a lot of very confident, very powerful language, but I also asked for help. If you cover up your weaknesses, I think you miss opportunities for human nature to want to kick in. At the end of the day, the guy ended up just wanting to help me. He didn't even believe in the idea."

Calling on the sales skills she learned in her cold-calling days, Blakely stood in department stores every day for two years talking to customers to sell her panties.

"I learned very quickly that my biggest challenge was location of the store -- (Spanx were) put in the sleepiest corner. I realized, 'This is going to come here and leave if I don't personally intervene, even if I have to sell every pair myself.' And that's basically what I did."

Photos: Sara Blakely: Underwear entrepreneur Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Sara Blakley is the creator of "body-shaping" underwear company Spanx. She turned a $5,000 start-up into into a multi-million dollar business -- becoming, according to Forbes, America's youngest self-made female billionaire in the process. Hide Caption 1 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Blakely founded Spanx in 1998, initially selling footless pantyhose through mail order and promoting them in person to department store customers. Hide Caption 2 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Blakely claims to have been inspired to create the product -- which she believed would sell millions -- by not liking the way she looked in white pants. Hide Caption 3 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Blakely says "having doors slammed in (her) face" during her previous job as a door-to-door fax machine saleswoman helped her cope with rejection from garment manufacturers and a lack of enthusiasm from department stores. Hide Caption 4 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Blakely says she took a hands-on approach after realising that Spanx products were only being made available in the least popular areas of department stores. She says she was later caught secretly moving her products closer to the checkout. Hide Caption 5 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Two years after Blakely founded the company, Spanx received an unexpected publicity boost from Oprah Winfrey, who named the underwear her favorite product of the year in 2000. Hide Caption 6 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Endorsements from celebrities including Julia Roberts followed and helped Blakely sell millions of pairs of Spanx. In recognition of her success, Blakely was names among Time magazine's 100 most influential people in 2012. Hide Caption 7 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Blakely remains the sole owner of Spanx, with underwear now on sale in more than 40 countries. Having generated a fortune -- estimated by Forbes magazine to be in excess of $1 billion -- she has given more than $20 million to charity through the Sara Blakely Foundation to help women through education and entrepreneurship. Hide Caption 8 of 9 Photos: Sara Blakely: Underwear entrepreneur Sara Blakely: Underwear entrepreneur – Today, Spanx produce a variety of products including active wear, menswear and swimwear. She attributes her success so far to extraordinary perseverance, salesmanship and risk-taking, saying: "The biggest risk in life is not risking." Hide Caption 9 of 9

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Blakely often snuck Spanx products relegated to the back of department stores closer to checkout, and spent nights stuffing shipping orders into padded envelopes. All while continuing her day job.

In 2000, just two years after launching the first rear-shaping prototype, Oprah Winfrey named Spanx her favorite product of the year. Blakely says was getting her hair highlighted when Oprah's studio called. She remembers jumping out of the chair and running out of the salon with all the foils still in her hair "having a full-blown happy attack -- dancing, cheering and clapping."

The unexpected publicity catapulted her to international acclaim. By 2012, she was listed as one of Time magazine's 100 most influential people

Fast forward to today and Blakely who is now mother to 3-year-old son, Lazer, says she balances her hectic work schedule with family life by "prioritizing, delegating and letting go."

Her motto is: "What if the Hokey Pokey really is what it's all about?" It's painted on a wall in all her homes and she says it reminds her to take life less seriously. It also helps her overcome extreme fears like flying --- one she faces regularly as she shuttles between her base in Atlanta and New York where her husband lives.

She says: "The biggest risk in life is not risking. Every risk you take in life is in direct proportion to the reward. If I'm afraid of something, it's the next thing I have to go do. That's just the way I've been."

Now, her main professional focus is "world butt domination through Spanx or Assets" (a cheaper line ). Already, over six million women wear the Spanx Power Panty, according to the company. She's also continuing to create new products --"the competition is watching us so closely" -- while dedicating resources to empowering women. The Sara Blakely Foundation has donated over $20 million to charity.

Blakely owns 100% of the business and says she has no plans to take the company public in the near future. Instead, she'd rather spend resources developing a product to fill another gap in the market.

"Before I retire, I want to make a comfortable high heel. I don't subscribe to the beauty is pain philosophy."

It might sound like a tall order, but for the Florida girl with no formal business qualifications who now shapes rears internationally, it might not be impossible.