Model You Never Knew Existed Shapes the Jeans You Wear

— -- J.Lo, Beyonce and Kim Kardashian may have the most talked-about derrieres in Hollywood, but when it comes to finding that perfect fit, 34-year-old Natasha Wagner influences the fashion industry more that those celebrities.

Wagner is a “fit model” for some of the world’s most popular denim brands, including Gap, Levi’s and 7 For All Mankind. She got the job by having the Goldilocks of behinds -- not too big, not too small. She’s perfectly average, and thanks to her, jeans have never looked so good on all of us.

“Fit models are probably the most important people that you’ve never heard of in the world of the denim industry,” Good Housekeeping’s style director Lori Bergamotto said on “Good Morning America.” “They’re not like runway models. What they’re looking for in a fit model is the perfect average. Basically what they want is somebody who’s slim, but has a curved bottom.”

Fit models act as live mannequins helping designers check fit, drape and appearance of their clothes before they hit the shelves, and industry insiders say when it comes to fit, Wagner has the best bottom in the country.

Denim’s it girl behind the seams is a size 6, has a 28-inch waist and stands at 5 feet 8 inches tall. She’s the most in-demand fit model for denim with a steady schedule.

“I’m definitely thin but curvy. Some of my clients have said I have all the curves in the right places,” Wagner said on “GMA” of her body. “I think it's perfectly imperfect. It’s perfect for what I do for my job.”

In addition to her good genes, Wagner keeps her size 6 by working out and eating right, and she said her clients are eager for her input.

“I think my feedback is often helpful for my clients,” she said. “I do this every day, all day long. I know exactly how a jean should fit.”

Wagner's story was first reported by Vogue.com.