world's greatest athlete

Short definition from Wiktionary

Noun

1. 1
   the Olympic champion male athlete in the men's decathlon athletics track and field sport
2. 2
   the Olympic champion female athlete in the women's heptathlon athletics track and field sport (the pentathlon was replaced by the heptathlon in Olympic competition for women)
3. 3
   the Olympic champion female athlete in the women's pentathlon athletics track and field sport (the heptathlon replaced the pentathlon in Olympic competition for women)