This list would not be complete without Shannon Miller, the most decorated gymnast in U.S. Olympic history. Miller made headlines in the early '90s by winning two Gymnastics World Championships in a row and winning gold at the 1996 Atlanta Olympics. Since she retired, she has taken upon herself the mission of fighting childhood obesity through education and awareness. The Shannon Miller Foundation sponsors a free running club for over 7,000 children ages 5-14 in the Jacksonville, Fla., area. Miller was also diagnosed with and beat ovarian cancer in 2011. In her book, "Competing with Cancer," she describes her journey from Olympic athlete to cancer survivor.