Jillian Michaels (born 18 February, 1974) is a fitness expert who gained prominence as a trainer on the NBC weight-loss reality series The Biggest Loser (USA). Michaels was the trainer for the red team until 2006, when she was replaced by Kim Lyons. She returned in 2007 as the black team coach, competing against Kim's red team and Bob Harper's blue team. Kim decided not to return for the spring 2008 season, leaving Jillian as the only female trainer. Along with Bob Harper, Jillian is also a trainer in the Australian version of the show. She began her career in exercise because she was considerably overweight before her teenage years (although not to the same extent as the contestants she whips into shape now). As a young adult, her mother enrolled her in a martial arts class, which was a new beginning for Jillian. Thereafter she dedicated herself to helping the overweight transform their lives and their bodies for the better.

Michaels' martial arts training includes the disciplines of Muay Thai and Akarui-Do, including experience with the use of nunchaku. She uses a blend of strength training techniques with her clients, including kickboxing, yoga, Pilates, plyometrics, and weight training.

According to her official homepage, "Jillian lives in Los Angeles with her beloved and faithful Chihuahua, Baxter. When she's not on the TV set, she enjoys traveling and getting involved in charitable activities. She is a celebrity advisor to National Day of Dance for Heart Health, an organization that encourages people to make exercise fun and to laugh, learn and dance to a healthier heart."

She is the youngest of the three trainers on the American Biggest Loser series; there is a nine-year gap between her age and rival trainer Bob's age, and she is also one year younger than one-time rival Kim.

Jillian Michaels currently hosts a Sunday talk radio show on Los Angeles' KFI (640 AM).

In the 2008-2009 holiday season, she will launch a new video game called Jillian Michaels Fitness Ultimatum 2009 for the Nintendo Wii. [http://www.realitytvworld.com/news/biggest-loser-trainer-jillian-michaels-star-in-wii-fitness-video-game-7295.php] [http://wii.ign.com/articles/889/889115p1.html?RSSwhen2008-07-14_152600&RSSid=889115]

Jillian is managed by Giancarlo Chersich