The most successful Olympic athlete of all time is Michael Phelps, a swimmer from the United States. He holds an incredible record of 23 gold medals, along with multiple silver and bronze medals, across four Olympic Games from 2004 to 2016. His dominance in various swimming events, particularly in individual medley and butterfly, has solidified his legacy as a sports icon. Phelps' achievements have also inspired future generations of athletes to pursue excellence in competitive sports.