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Jordyn Wieber, gymnastics (United States)
The reigning all-around world champion and two-time defending U.S. all-around champion, Wieber, 17, is a favorite to add the Olympic all-around gold to her collection. She also led the U.S. to its third team gold and took bronze on her favorite event, the balance beam, at worlds. Wieber won three all-around golds in 2012 before coming in second to Gabby Douglas at trials.