NAM Y. HUH—AP

Rau'Shee Warren, 21, Boxing

As a kid in Cincinnati, Rau'Shee Warren had a choice: hit the gym, or maybe end up in jail. "The older guys would go around, punchin' on people for no reason," he says. "That's when I realized that boxing was good for me." At 17, Warren was the youngest member of the U.S. team at the last Games in Athens, Greece. He lost in the first round. Now, he's the flyweight favorite after winning the world title last year. Warren is the first U.S. boxer to compete in back-to-back games in 32 years. Why didn't he go pro like other boxers? "Gold medal," he says. "Gold medal. That's all that's been on my mind. I know how the Olympics feels. I know the ring. I know the judges. I know how to fight for the judges. I'm ready."

--By Sean Gregory