Neethling is the first South African to compete in four successive Olympic Games and also an Olympic gold medalist. The highlight of his exceptional career was the Olympic gold medal he won in the 4×100 metres freestyle relay at the 2004 Summer Olympics in Athens. He is also a former member of the team which held the 4×100m freestyle relay world record, and he holds several South African records.
Neethling holds multiple world records. In November 2005, he announced that he had refused a R50 million offer to switch nationalities and swim for Qatar in the 2008 Beijing Olympics. Born in Bloemfontein, he attended Grey College, where he excelled in swimming, earning a place in the South African swimming team for the 1996 Summer Olympics in Atlanta, where he came fifth in the 1,500m freestyle. In 2015 he donated his Olympic gold medal to his old school.
Immediately following Atlanta he enrolled at the University of Arizona where he was nine-times NCAA National Champion, 1999 NCAA Swimmer of the Year and University of Arizona Athlete of the Century.
He currently (Feb 2016) holds the South African record for the 200m, 400m, 800m and 1500m.