In 2008, Phelps had arguably the most dominating single Games performance in Olympic history, winning a record eight gold medals. After a tabloid scandal and disappointing results in 2010, many wondered if Phelps still had the desire to push himself to his peak. He has since had a resurgence in 2011, but will be tested in London like never before by teammate Ryan Lochte among others.
2 of 47Bob Martin/SI
In 2008, Bolt broke both the 100m and the 200m world records, doubling in Beijing. But since that time American Tyson Gay and others have gotten closer to Bolt -- Gay even defeated him in 2010. Though Gay is injured and won't compete at this summer's World Championships in South Korea, Bolt is looking beatable this year.
3 of 47Heinz Kluetmeier, Bob Martin/SI(2)
Few in London will have the crowd behind them like Adlington, Great Britain's first swimmer to win two gold medals since 1908. Since Beijing, Adlington has had her ups and downs, but as long as the pressure of being Britain's great swimming hope does not get to her, the older and more mature Adlington could surpass her totals from 2008.
4 of 47Bob Martin, Robert Beck/SI
Sir Chris Hoy
Hoy (Sir Chris Hoy, in fact) won three gold medals in 2008, making him the most successful British Olympian in a century. The Scotsman will be 36 next summer, and while he may be past his prime, the crowd in the Velodrome should be able to help him secure at least one gold medal.
5 of 47John W. McDonough, Heinz Kluetmeier/SI
Lochte, who is one year older than Michael Phelps, has been coming on strong since winning four medals in 2008. If the fact that he won six gold medals at the 2010 Short Course World Championships and beat Phelps Tuesday in the 200-meter finals at the World Championships, Lochte could be the reason for Phelps receiving his first-ever silver medal.
6 of 47Greg Nelson/SI
Having finished third and second in the all-around at the 2010 and 2009 World Championships, respectively, Bross will likely be the cornerstone of the United States' women's gymnastics team.
7 of 47Elise Amendola/AP; Alfred/DPPI-SIPA/Icon SMI
Nadal is the reigning Olympic champion in men's singles. He, Roger Federer and Novak Djokovic have all had their fair share of success at Wimbledon (the site of the event) in the past, making the Olympic tournament a dynamite draw.
8 of 47Bill Frakes/SI
Despite the fact that she has won the 200m in the World Championships three consecutive times, Felix will be just 26 years old next summer. How she does attempting a 200-400 double at this summer's World Championships will be a good indicator for London.
9 of 47Xinhua/Imago/Icon SMI
Williams is still recovering from blood clots in her lungs and recently made her return to tennis at Wimbledon. But she and her sister Venus may be blocked from participating in London if they can't take part in the qualifiers. The Williams sisters have won doubles gold in Sydney and Beijing.
10 of 47Bill Frakes/SI
The reigning champion in the 5000m and the two-time reigning champion in the 10,000m, Bekele is arguably the greatest long distance runner in history. He will only be 30 years old next summer, so as long as he is able to fully recover from a 2010 calf injury, it should be another memorable Olympics for the Ethiopian, who holds the world records in both the 5000m and 10,000m.
11 of 47AFLO Sport/Icon SMI; Faugere/DPPI-SIPA
Isnbayeva, considered by many to be the greatest pole vaulter of all-time, will be a heavy favorite when she gets to London. She has won two gold medals ('04 and '08) and is a five-time World Champion.
12 of 47Bob Martin/SI
Semenya is a middle-distance runner who won gold in the women's 800 meters at the 2009 World Championships. After her dominating victory, Semenya's critics claimed that she had a physical condition that gave her an advantage over other female racers. The IAAF controversially gave Semenya gender tests and she wasn't allowed to participate in certain events in 2010. Semenya has since been cleared to race in any future events including the Olympics.
13 of 47John Biever/SI; Sergey Ponomarev/AP
In 2008, Mitcham became the first Australian male to win an Olympic gold medal in diving since 1924. He dominated the 10-meter platform, finishing with the highest single-dive score in Olympic history. The 23-year-old Mitcham is one of a handful of openly gay athletes competing in the Olympics, though he missed the recent World Championships due to an abdominal injury.
14 of 47Bob Rosato/SI
The Heat guard/forward was one of the United States' major contributors in its gold medal run in the '08 Olympics. A unique combination of size and athleticism, James is capable of playing and defending multiple positions. In 2010, the two-time NBA MVP notoriously left his hometown Cleveland Cavaliers for the Heat, significantly damaging his popularity in the United States.
15 of 47Bill Frakes/SI
The 37-year-old Radcliffe currently holds the women's marathon world record. In 2003, she finished a race with a time of 2:15:25, a mark that still stands. Radcliffe has won 12 gold medals in a variety of international championships but has never medaled at the Olympics.
16 of 47Bob Martin/SI
Ennis is one of the world's best track and field stars, primarily in the heptathlon and pentathlon. She won her first gold medal for the heptathlon at the 2009 World Championships in Berlin. She has since won gold in the heptathlon as well as a gold in the pentathlon in the 2010 World Indoor Championships. In 2010, Ennis set championship records in both events, but only the heptathlon is part of the Olympic program.
17 of 47Heinz Kluetmeier/SI
The French swimmer is probably most known for getting caught in the anchor leg of the 4x100 freestyle relay by Jason Lezak of the U.S. That win gave Michael Phelps his record-breaking eighth gold medal. Bernard came back to win gold in the 100-meter freestyle, beating Lezak and providing some redemption.
18 of 47Robert Beck/SI
The British racer has won three gold medals and six Olympic medals overall during his exceptional career. In the 2008 Olympics, Wiggins won gold in both the team pursuit and 4km individual pursuit, though the latter is no longer an Olympic event.
19 of 47Xinhua/Imago/Icon SMI
Most people's focus may be towards a Federer-Nadal clash in singles, but keep in mind that Federer is the defending Olympic men's doubles champion with countryman Stanislas Wawrinka.
20 of 47Simon Bruty/SI
Coughlin is one of the most successful female swimmers in U.S. Olympic history, compiling 11 medals over her illustrious career. In 2008, she became the first American woman to win six medals in one Olympics. She also became the first woman to ever win gold in the 100m backstroke in consecutive Olympics. Coughlin will enter the 2012 Games against heavy competition to defend her backstroke crown.
21 of 47Al Tielemans/SI
The 22-year-old Uchimura is one of the rising stars of the international gymnastics world. At the age of 20, he won the individual all-around championship at the 2009 World Artistic Gymnastic Championships. He repeated this feat the next year. The 2012 Games will be Uchimura's second Olympic competition.
22 of 47Elaine Thompson/AP
Moore was the No. 1 pick in the 2011 WNBA Draft and a four-time All-America at the University of Connecticut. She joins a U.S. team that has dominated its competition in previous Olympics.
23 of 47Mike Powell/SI
The Isle of Man resident burst onto the international racing scene in the 2008 Tour de France when he won four stages, something that had never been done by a British racer. He's continued to dominate the Tour's sprints and now owns 20 career stage wins. The 26-year-old has never medaled in the Olympics, but his performances in other international competitions make him a racer to watch in 2012.
24 of 47Al Tielemans/SI
Horton led Team USA to a bronze medal in the 2008 Olympics, winning the silver medal for himself in the high bar. A two-time national all-around champion, the USA's top gymnast will defend his title at the Visa Championships in August.
25 of 47Robert Beck/SI
Kerri Walsh and <br> Misty May-Treanor
Since teaming up in 2004, May-Treanor and Walsh have been called "the greatest beach volleyball team of all time." After winning in Athens and Beijing, they are the only beach volleyball team to repeat as gold medalists. After not playing in 2009 due to injuries and the birth of Walsh's two sons, the duo took a disappointing second place in this year's volleyball world championship.
26 of 47Simon Bruty/SI
Gay is the fastest man in the United States, holding the U.S. record for the 100 meters. His fans argue that his 2010 victory against the world's fastest man Usain Bolt in Stockholm closes the gap between the two, but a hip injury prevented them from meeting again this year. We'll just have to wait until London.
27 of 47Bill Frakes, Peter Read Miller, Al Tielemans/SI
The point margin separating Clay's gold-medal performance in Beijing from other medalists was the widest since 1972. After a year hiatus to rest mentally and recover from an injured hamstring, he is back training for a third Olympic competition. Clay recently proved his continuing athletic prowess when he won the gold in the heptathlon at the 2010 World Indoor Championship.
28 of 47Bill Frakes/SI
After the humiliation of failing to qualify for the Beijing Olympics, Jeter changed coaches and re-evaluated her race tactics. One year later, she was the fastest woman in the world; her time of 10.64 at the Shanghai Golden Grand Prix in 2009 is second alltime only to Florence-Griffith Joyner.
29 of 47Bob Martin/SI
Jackson is a three-time WNBA MVP and 2010 Finals MVP who plays for the Seattle Storm. She was the youngest player to score 3,000 and 4,000 points in WNBA history. With the exception of the 1992 Olympics, the U.S. team has dominated the Olympics since 1984. Australia has challenged them for the last three tournaments, Jackson playing in each championship game. 2012 will be her fourth Olympic tournament. Will it be her final?
30 of 47Simon Bruty/SI
The former WTA Tour World No. 1 has yet to win a Grand Slam title but will be in the mix at the Wimbledon event.
31 of 47Peter Read Miller/SI
In Bryan Clay's absence, Hardee won the decathlon at the 2009 World Championship in Berlin. He then finished second to returning Clay in the heptathlon at the 2010 World Indoor Championship, although trailing by a mere 20 points. Whether or not Hardee can overcome Clay in London, the two, along with decathlete Ashton Eaton, hope for a USA sweep of the medals.
32 of 47John Biever/SI
Gasol led Spain to its second silver medal in Olympic basketball history in 2008 when Spain fell to the United States in the finals 118-107. He'll likely go up against Laker teammate Kobe Bryant at the 2012 Games.
33 of 47Chris Keane/Reuters
The 16-year-old Franklin holds the American record in the 200-meter backstroke, and will be one of the young faces to watch on the United States team.
34 of 47John Biever/SI
Daley finished seventh in the 10-meter platform at the 2008 Summer Olympics when he was 14 years old. Since then, he's won the FINA Championship for the 10-meter platform and is preparing for a run in his home country. Daley faced tragedy in May when his father lost a five-year battle with cancer.
35 of 47Robert Beck/SI
Phil Dalhausser and <br> Todd Rogers
Dalhausser and Rogers have won five straight AVP Tour Championships and are the reigning gold medalists in beach volleyball.
36 of 47Philippe Millereau/DPPI/Icon SMI
The 16-year-old Russian suffered an ACL tear in April that will likely keep her out of the World Championships in October. Mustafina won the 2010 All-Around World Championship, and will be a major threat for the all-around title in London if healthy.
37 of 47Bill Frakes/SI
Oliver missed out on the silver in the 110-meter hurdles in Beijing by .01 seconds to fellow countryman David Payne. He did, however, grab the gold medal in September's IAAF Continental Cup with a time of 13.11.
38 of 47Heinz Kluetmeier, Simon Bruty/SI
At age 44, Torres is already the oldest swimmer to the make the U.S. Olympic team and now she's trying to break her own record in London (that'll make six Olympic games). She'll look to add to her 12-medal collection, which includes four golds.
39 of 47John W. McDonough/SI
The Notre Dame product has won back-to-back gold medals in the individual sabre for the United States. Zagunis won the 2010 World Championships and is the odds-on favorite to take the individual title in London.
40 of 47John W. McDonough, Heinz Kluetmeier/SI
Mellouli is the reigning gold medalist in the 1500-meter freestyle. In his off-time, the Tunisian is a graduate coach at his alma mater Southern Cal. It's rumored that in 2012 he'll go after the 400-meter freestyle, an event he won the silver medal in during the 2009 World Championships.
41 of 47Andy Wong/AP
Emanuel Rego and Alison Cerutti
Emanuel and Alison are the men's beach volleyball team to beat after the Brazilian pair won the 2011 World Championships in June 2011. Emanuel already has two Olympic medals -- gold in 2004 and bronze in 2008 -- after having previously partnered with Ricardo Santos.
42 of 47Bob Martin/SI; Kai Pfaffenbach/Reuters
The U.S. team must win its region to qualify for the Olympics. If it does, it will be one of the favorites along with Brazil and World Cup champion Japan. Solo was a standout in Beijing, shutting out Brazil 1-0 in the gold-medal game.
43 of 47Bob Martin/SI
Having already won The Bowerman -- track and field's version of the Heisman Trophy -- for his dominance in the decathlon, the recent Oregon graduate will be looking to land a stop on the podium in London. To do so, he will have to compete with fellow Americans Bryan Clay and Trey Hardee, the reigning Olympic and world champions, respectively.
44 of 47Emanuele Pennacchio/Action Plus/Icon SMI
Larissa Franca and Juliana Silva
If anyone is to beat the seemingly unstoppable team of Walsh and May-Treanor, it's Larissa and Juliana. The Brazilians are coming off a gold-medal performance in the 2011 World Championships that saw them defeat the American tandem 2-1 in the finals.
45 of 47John W. McDonough/SI
The NBA Rookie of the Year made the highlight reel nightly during this past season, but will he be able to make the U.S. starting squad?
46 of 47Chuck Burton/AP
Wu finished fourth in the 200 fly at the 2008 Olympics, but defeated Phelps in the event twice in 2011, including Grand Prix meets in Charlotte and Michigan. Before Wu's victory, Phelps had not lost in the 200 fly in nine years.
47 of 47Sergey Ponomarev/AP
Rhode took the gold in Atlanta (where she was the youngest member of the U.S. Olympic team at 16) and Athens and grabbed bronze in Sydney and silver in Beijing. She has a chance to be the first American athlete to medal in five straight Olympics in an individual sport.
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