Making her Olympic debut in 2012 at 15 years old, Katie Ledecky won gold in the women’s 800m freestyle by more than four seconds – but that was only the beginning of her success. She went on to dominate the distance events over the next few years, becoming the first swimmer to win the 200m, 400m, 800m and 1500m freestyle titles at a single world championship in 2015. The feat became known as the “Ledecky Slam.”