Michael Phelps, the most decorated Olympian and swimming legend, celebrates his 35th birthday on June 30, 2020 (Tuesday). Phelps holds the record for most medals won at Olympic events, most gold medals in Olympics and also the highest number of medals in a single Games event. Phelps, who first rose to fame after breaking a United States national swimming record at 15, retired in 2016 as the most successful swimmer in Olympics history.