The self-described "most famous health and fitness guru in America," David Kirsch is best known as the guy who got Heidi Klum ready for the Victoria's Secret runway just eight weeks after she gave birth.

Kirsch started out his career as a lawyer and spent four years practicing the profession, before switching gears and opening his first gym, the Madison Square Club, in 1991. Over the next decade, Kirsch assembled a celebrity-heavy clientele, people like Naomi Campbell, Kerry Washington, Anne Hathaway, and Ellen Barkin (to name a few). But his most famous client in recent years has been Heidi Klum. When the supermodel-turned-reality show host gave birth to her second child in 2005, she had just a few weeks to get back in shape for a Victoria's Secret shoot or risk losing the contract. She flew Kirsch to LA, he put her on a crash diet and exercise plan, and she managed to make the cut.

Kirsch's gym, which overlooks Madison Square Park, is one of the ritziest around: Wealthy clients (like restaurateur Danny Meyer) shell out up to $20,000 annually for Kirsch's medicine ball workouts and nutrition advice. No need to worry about gym overcrowding: only six people are allowed to work out simultaneously. Kirsch's empire is ever-expanding: in addition to a handful of fitness books (Sound Mind, Sound Body, The Ultimate New York Body Plan, The Ultimate New York Diet), he now has a food delivery service, a line of skin care products, and a line of nutritional supplements. He's also a fitness-segment fixture on shows like Extra, Access Hollywood, and the Today Show. [Image via AP]