Inventor of SPANX Makes Billionaire’s List It widely known that celebs rely on the body smoothing undergarments called SPANX, especially when walking the red carpet. Kim Kardashian calls them "her best friend" and Oprah Winfrey (who boosted the brand on her show) enthuses she's "given up panties. I wear SPANX!" Screen goddesses (and mere mortals) love them so much in fact, that the company's fou…