In her short, but spectacular career, she was regarded as one of the most exciting and successful young swimmers in the world and was expected to have a long and successful career, but a serious shoulder injury forced her to retire in December 2018 at the age of just 23.

She was elected to the Laureus World Sports Academy and was inducted at the 2019 Awards Ceremony in Monaco.

At her Olympic debut in London in 2012, aged 17, she had won four gold medals and a bronze, sweeping the backstroke events, winning both 100 and 200 metres. Her successes earned her a second straight Swimmer of the Year Award from FINA, world swimming’s governing body. She also won Swimming World's World Swimmer of the Year Award for 2012.

A year after London, she was the sensation of the World Championships in Barcelona, becoming the first woman in history to win six titles at a single World Championships, taking gold medals in three individual and three relay events. For this achievement she became the youngest ever winner of the Laureus World Sportswoman of the Year Award, at 18, beating the former youngest winner, Serena Williams, who was 21 when she received the Award.

At the 2016 Olympics in Rio de Janeiro, with her injuries beginning to affect her, she swam in the 200m freestyle and 200m backstroke heats, but did not make the finals. However, she did receive her fifth gold medal in the 4 × 200m freestyle relay for swimming in the heats.

Missy was born in Pasadena, but her family settled in Denver, Colorado. She is 6ft 1 ins (185 cm) tall and has women's size 13 feet: "We call them built-in flippers," says her father. Missy is a devout Christian and is committed to being a positive role model for young athletes in all sports.

During her rise to stardom, she continued to refuse prize money and endorsements so that she could maintain her amateur status to compete in college, where she attended the University of California, Berkeley.