As of my knowledge cutoff in September 2021, the most successful decathlete in Olympic history is Ashton Eaton of the United States. While there is no equivalent heptathlete with a comparable level of success, Eaton's achievements in the decathlon are unparalleled.
Ashton Eaton participated in the decathlon at the 2012 London Olympics and the 2016 Rio de Janeiro Olympics. In both Games, he emerged as the gold medalist, solidifying his status as the most successful decathlete in Olympic history.
At the 2012 London Olympics, Eaton set a new Olympic record with a total of 8,869 points, surpassing the previous record set by Roman Šebrle. He delivered consistent performances across the ten events, demonstrating his versatility and mastery of the disciplines.
Eaton's dominance continued at the 2016 Rio de Janeiro Olympics, where he defended his title and won his second consecutive gold medal in the decathlon. Although he fell short of his own world record, Eaton's total of 8,893 points showcased his exceptional skills and competitiveness.
What sets Eaton apart is not only his Olympic success but also his world record performances. He broke the decathlon world record twice during his career. First, in 2012, he set a new world record with 9,039 points at the U.S. Olympic Trials, surpassing the previous mark held by Roman Šebrle. Then, at the 2015 World Championships in Athletics, Eaton further improved the record, reaching a remarkable total of 9,045 points.
Regarding the heptathlon, it is important to note that there is no single athlete who has achieved a comparable level of dominance or success as Eaton in the decathlon. The heptathlon event is exclusively for women, and while many exceptional athletes have competed in it, there isn't a standout performer who can be considered the most successful heptathlete in Olympic history to the same extent as Eaton in the decathlon.
Update: Kevin Mayer holds the world record with 9126 points.
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