Michael Phelps, U.S. The Athens star again can win eight medals at one meet, but he'll be swimming two events--the 100- and 400-meter free--for the first time at a major international competition.
Katie Hoff, U.S. After winning three races (200 free, 200 IM, 400 IM) at the world trials this month, the 16-year-old Baltimore high schooler will shoot for her first international title.
Brendan Hansen, U.S. The world-record holder in the 100- and 200-meter breaststroke will try to better the silver and bronze medals he won in those races, respectively, at Athens.
Grant Hackett, Australia The distance ace can make history in the 1,500 free by becoming the first swimmer to win gold in the same event at four world championships.
Luo Xuejuan, China China's only 2004 Olympic swim champ (100-meter breaststroke) suffered a severe allergic reaction to pain medication after she turned an ankle last month. --Brian Cazeneuve