Welcome to ESPN's fan vote, where you, the reader and sports fan, will decide which individual or team has been the most dominant in the 21st century.
In our latest match-up, we have the King of Wimbledon Roger Federer against Simone Biles, this century's most celebrated gymnast.
(Please vote in the poll at the bottom of this page to decide the winner.)
Roger Federer at Wimbledon (2003-2007)
Roger Federer's breakthrough at a major came when he won his first Grand Slam title at Wimbledon in 2003 at the age of 21. The win was followed by his rapid rise, soon after which he was ranked World No. 1 for the first time ever in February 2004. Such was his dominance that he ended up holding the position for 237 weeks in succession.
During that time, it was his invincibility on grass that stood out, as he won a staggering 65 straight matches on the surface. His silky forehands and effortless volleys enabled him to win every edition of Wimbledon from 2003 to 2007 -- becoming only the second man after Bjorn Borg to win five successive titles at the Championships in the Open era.
Simone Biles at World Championships (2013-present)
Simone Biles will have to wait another year if she is to add to her haul of four Olympic golds, but her dominance on the World Championships stage has already firmly placed her among the all-time great gymnasts.
Biles, who began her senior career at 16, won two golds (all-around, floor) at her first World Championships in Antwerp in 2013. She followed that with four golds each at the next three Worlds in 2014 (Nanning), 2015 (Glasgow) and 2018 (Doha), and then won five golds (team, all-around, vault, beam, floor) at the Stuttgart World Championships last year.
Biles' 25 World medals -- she also won three silver and three bronze medals along the way -- are the most by any gymnast, male or female. While Vitaly Scherbo's previous record of 23 medals (12 golds among them) stood for over two decades, Biles' feats too will take some beating.
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