1 of 19 Jamie Squire/Getty Images
Michael Phelps, swimming (United States)
Phelps — the first U.S. male swimmer to compete in four Olympics — won't duplicate his eight gold medal-winning heroics from Beijing (he qualified in the same eight events, but will only swim seven), but history is still on the line. The 16-time medalist needs just three medals of any color to dethrone Russian gymnast Larisa Latynina as the most decorated Olympian of all time. And of course, the 14-time Olympic champ can extend his own record for the most gold medals. Just make sure you don't miss him chasing history: Phelps will retire after London.
2 of 19 Chris Trotman/Getty Images
Jordyn Wieber, gymnastics (United States)
The reigning all-around world champion and two-time defending U.S. all-around champion, Wieber, 17, is a favorite to add the Olympic all-around gold to her collection. She also led the U.S. to its third team gold and took bronze on her favorite event, the balance beam, at worlds. Wieber won three all-around golds in 2012 before coming in second to Gabby Douglas at trials.
3 of 19 Frederic J. Brown/AFP/Getty Images
Ryan Lochte, swimming (United States)
While his good pal Michael Phelps took a lengthy sabbatical after Beijing, Lochte, who's competing in his third Games, became the man of the pool. The six-time medalist and defending 200-meter backstroke champ dominated the 2011 World Championships, winning five golds and one bronze, and defeated Phelps in both head-to-head races. At the Olympic trials, he beat Phelps in the 400-meter individual medley for the first time (Phelps is the two-time defending Olympic champ in the event), but Phelps won their next three head-to-head match-ups. To be settled in London? You bet.
4 of 19 Gabriel Bouys/AFP/Getty Images
Usain Bolt, track and field (Jamaica)
Can lightning strike twice? Bolt lit up the track in Beijing with his world record-setting runs in the 100-meter and 200-meter sprints and will try to become the first man to defend both titles. But perhaps some cause for concern: He finished second in both distances to Yohan Blake at trials and withdrew from a tuneup because of injury.
5 of 19 Jamie Sabau/Getty Images
Holley Mangold, weightlifting (United States)
Mangold, the younger sister of New York Jets center Nick Mangold, is the second-ranked overall lifter in the country and only began weightlifting in 2008. She previously played high school football as an offensive linesman and was featured on a 2011 episode of MTV's True Life.
6 of 19 Quinn Rooney/Getty Images
James Magnussen, swimming (Australia)
The brash sprinter became Australia's first 100-meter world champion last year and produced a statement swim at March's Australian National Championships with a blistering 47.10 — 19-hundredths off the world mark set by Brazil's Cesar Cielo Filho in 2008. The time is also the fourth-fastest in history and the fastest this year.
7 of 19 Christian Petersen/Getty Images
Lolo Jones, track and field (United States)
London is about redemption for Jones. The track star, who made headlines recently after revealing that she's still a virgin at 29, was on her way to gold in the 100-meter hurdles in Beijing when she clipped the penultimate hurdle and fell back to seventh. She rebounded to defend her 60-meter hurdles world indoor title in 2010 and secured her Olympic spot by finishing third at trials.
8 of 19 Al Bello/Getty Images
Missy Franklin, swimming (United States)
Poised to be the next big American swimming star, Franklin will compete in seven events in her first Olympics. The 17-year-old burst onto the scene in 2010 and last year won five medals (three gold, one silver, one bronze) at the world championships. In October, she became the first female swimmer to set a world record since high-tech bodysuits were banned in January 2010. If Franklin medals in all of her events, she would surpass teammate (and Dancing with the Stars alum) Natalie Coughlin for the most medals won by an American female in one Olympics; Coughlin won six in 2008.
9 of 19 Gabriel Bouys/AFP/Getty Images
Ashton Eaton, track and field (United States)
A five-time NCAA champion, Eaton blew away the decathlon field at trials, where he broke Roman Sebrle's 11-year-old world record with 9,039 points. He is only the second person after Sebrle to exceed the 9,000-point mark. In doing so, Eaton also eclipsed Dan O'Brien's American record of 8,891 points, set in 1992.
10 of 19 John Thys/AFP/Getty Images
Aliya Mustafina, gymnastics (Russia)
Mustafina has been on the comeback trail after missing much of the 2011 season from an ACL tear. Prior to that, she won three silvers and two golds, including the all-around, at the 2010 World Championships.
11 of 19 Christian Peterson/Getty Images
Allyson Felix, track and field (United States)
All that's missing from Felix's sterling resume — which includes three world championship titles — is an Olympic gold medal in the 200 meters (aka her "baby"). She finished second to Jamaica's Veronica Campbell-Brown the past two Olympics, but served notice at trials with a time of 21.69 — the fourth-fastest ever. She'll also compete in the 100 meters, a spot she secured after her teammate and training partner Jeneba Tarmoh withdrew from a runoff, which had been planned after the two tied for the third Olympic spot.
12 of 19 Ronald Martinez/Getty Images
John Orozco, gymnastics (United States)
The 19-year-old, who was taunted by kids in his native Bronx for doing gymnastics, won the all-around at nationals, edging out Danell Leyva. Leyva returned the favor at trials, beating Orozco by .95, setting up what could be a dynamic showdown in London. Fun fact: Orozco appeared in Gym Class Heroes' "The Fighter" music video and was an extra on three episodes of Law & Order.
13 of 19 Clive Rose/Getty Images
Ye Shiwen, swimming (China)
China's newest swimming sensation stunned the 200-individual medley field last year to win her country's first world championships gold medal. At 15, Ye was the youngest gold medalist by more than five years. She followed up with four gold medals at the Chinese Nationals and was named 2011's Pacific Rim Female Swimmer of the Year.
14 of 19 Adrian Dennis/AFP/Getty Images
Justin Gatlin, track and field (United States )
After serving a four-year ban for a positive doping test, forcing him to miss Beijing, the 2004 100-meter champ is back and running faster than ever. Gatlin won trials with a personal best time of 9.80 seconds, which ties him for seventh-fastest all time and is the fastest for a man over 30.
15 of 19 Mike Stobe/Getty Images
Yohan Blake, track and field (Jamaica)
Blake may just steal Usain Bolt's thunder in London. At 19, he became the youngest man to run sub-10 seconds in the 100 meters and last year, at 21, he became the youngest world champion in the distance. (Bolt was disqualified.) Later that year, Blake posted the second-fastest time ever in the 200 (19.26), behind Bolt. At trials, he bested Bolt in both distances and notched the fourth-fastest time ever in the 100 (9.75).
16 of 19 Ezra Shaw/Getty Images
Qiu Bo, diving (China)
The 19-year-old phenom is the reigning world champion in the 10-meter platform, which he won with 609.20 points, becoming the first diver to break the 600-point barrier. The 10-m platform was the only diving event of eight that China did not win in Beijing. (It swept all eight at worlds.)
17 of 19 Ezra Shaw/Getty Images
Gabby Douglas, gymnastics (United States)
Douglas made the battle for all-around gold very interesting when she dethroned favorite Jordyn Wieber for the top spot at trials. The bubbly 16-year-old was also part of last year's world championship team and won gold on uneven bars at nationals.
18 of 19 China Photos/Getty Images
Kerri Walsh and Misty May-Treanor, beach volleyball (United States)
Arguably the best beach volleyball team of all time, Walsh and May-Treanor, who were the first beach volleyball players to win two golds, will look to three-peat in London. They're no longer the dominant, unbeaten force they once were, but they are still the No. 3-ranked pair in the world. May-Treanor will retire after the Games.
19 of 19 Toussaint Kliiters/AFP/GettyImages
Oscar Pistorius, track and field (South Africa)
Known as the "Blade Runner," Pistorius will be the first double-amputee to run at the Olympics. A four-time Paralympics gold medalist, Pistorius first started competing against able-bodied athletes in 2007, but he was temporarily banned and ruled ineligible for Beijing by the International Association of Athletics Federation, which claimed that his carbon fiber blades gave him an unfair advantage. The Court of Arbitration for Sport overturned the ban, ruling that no advantages have been found, but Pistorius failed to qualify for Beijing. He will compete in the 400 meters and the 4x400-meter relay. Pistorius' best time in the 400 this year (45.20) ranks him in the top 35.