Body of Work: The Top 20 Fitness Icons

The Good Cop: Bob Harper

He is The Biggest Loser's beating heart, a tattooed hunk who helps change lives on TV. In 2004, Bob Harper, then a trainer and Spinning instructor in Los Angeles, answered a casting call for a weight-loss reality show.

"I remember being turned off by the title," he recalls. "I wanted to make sure the show depicted obese Americans in the best possible light." Now in its 13th season, The Biggest Loser is a six-day-a-week commitment, yet Harper still finds time to teach a Saturday group fitness class at Crunch and work on his growing product line, which includes supplements, an interactive website, and his book The Skinny Rules: The Simple, Nonnegotiable Principles to Getting to Thin. (Rule 18: "Go to bed slightly hungry.")

Harper's current fitness crush is CrossFit, the interval workout program that includes a lot of reps and plyometrics. "I've put on more muscle," he says of his new regimen's effect. "I shot the cover for a men's magazine, and when I saw it, I thought, Whoa, that's pretty good for a 46-year-old man!"