 Tom Brady who topped the list. The longtime New England Patriots quarterback only came in fifth. Simone Biles, Roger Federer, and LeBron James were all in the top ten, but they weren't number one. Even the great Serena Williams came in second to 23-time Olympic gold medal swimmer Michael Phelps, dubbed the number one athlete of the 21st century by ESPN. ABC's Sherry Preston. This is the story of the one.