Michael Phelps: He will return to the Olympics for the fifth and possibly final time Simone Biles: Just 19, she's the first woman to win three consecutive world all-around titles Justin Gatlin: The sprinter will try to unseat Usain Bolt as the fastest man in the world Ibtihaj Muhammad: She is currently the second-ranked women's fencer in America Ashton Eaton: He is favored to be the first two-time defending decathlon champion Alex Morgan: She is the clear leader of the U.S. women's national soccer team Kevin Durant: Without Steph Curry or LeBron James in the lineup, he is seen as a leader for the U.S. Men's Basketball team Allyson Felix: She's recovering from an ankle injury, but is still expected to be a strong contender Katie Ledecky: She is going for gold in the 200m, 400m and 800m freestyles in Rio Serena Williams: The 34 year old four-time gold medalist may decide that this is her final Olympics appearance