When Forbes magazine released its annual list of billionaires this week, a new face was featured on the issue's cover: Sara Blakely, who at 41 is the youngest self-made female billionaire ever to appear on the list. Blakely is the founder of Spanx, the slimming hosiery line that "reinvented the girdle," says Forbes' Claire O'Connor. A former saleswoman and amateur standup comedian, Blakely did it all on her own, with a $5,000 initial investment and years of grueling work. Spanx now sells 200 products in more than 11,000 stores in 40 countries. Here, a guide to Blakely's "impressive" rise:

How did Spanx start?
Like other successful inventors, Blakely discovered that "the product she needed didn't exist," says Belinda White at Britain's The Telegraph. Once, a pair of cream slacks threatened to show her pantyline — so she snipped off the feet of her pantyhose and wore that instead. "But they rolled up my legs all night," she tells Forbes. "I remember thinking, 'I've got to figure out how to make this.'"

How did Spanx catch on?
Even while she maintained a nine-to-five job selling office supplies, Blakely found time to pitch her product to Neiman Marcus and other department stores. It was a hit, making women look as if they'd "dropped a dress size," says White. Blakely's big break came in 2000, when Oprah Winfrey featured Spanx on the "annual audience scream-a-thon that was her Favorite Things Show," says O'Connor.

What is Spanx worth?
Pulling in $250 million in revenue a year, Spanx is estimated to be worth $1 billion. Blakely is the sole owner of the company, which has no debt and has never received outside investment.

What's in store for Blakely?
She's not resting on her laurels. Spanx is expanding its global reach, while diversifying its offerings beyond hosiery. "I think my story says that, when women are given the chance and the opportunity, that we can achieve a lot," Blakely tells CBS News. "We deliver. We can make the world a better place, one butt at a time."

Sources: CBS News, Forbes, TheMarySue, The Telegraph