Thousands of athletes from more than 200 countries will be competing in this year's Summer Olympics.

Here are 25 who we will be watching closely as the Games progress. Some, like Simone Biles above, are already global superstars. Some you might be hearing about for the first time.

<strong>Naomi Osaka (Japan):</strong> Osaka, one of the biggest stars in tennis, recently made headlines when she <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F05%2F31%2Ftennis%2Fnaomi-osaka-french-open-withdraw-spt-intl%2Findex.html" target="_blank">withdrew from the French Open,</a> citing her mental health. The four-time major winner also sat out Wimbledon. But the 23-year-old will be competing in her home country for the Olympics.
Naomi Osaka (Japan): Osaka, one of the biggest stars in tennis, recently made headlines when she withdrew from the French Open, citing her mental health. The four-time major winner also sat out Wimbledon. But the 23-year-old will be competing in her home country for the Olympics.
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<strong>Katie Ledecky (United States):</strong> Ledecky was one of the biggest stars of 2016, winning five Olympic golds and setting two world records — one in the 400-meter freestyle and one in the 800-meter freestyle. She was the first swimmer since 1968 to win the 200-, 400- and 800-meter freestyles at the same Olympics, and she will be looking to defend all of those titles in Tokyo. She will also be favored in the 1,500-meter freestyle, which is making its debut this year on the women's side. Ledecky, 24, has broken 14 world records during her illustrious career.
Katie Ledecky (United States): Ledecky was one of the biggest stars of 2016, winning five Olympic golds and setting two world records — one in the 400-meter freestyle and one in the 800-meter freestyle. She was the first swimmer since 1968 to win the 200-, 400- and 800-meter freestyles at the same Olympics, and she will be looking to defend all of those titles in Tokyo. She will also be favored in the 1,500-meter freestyle, which is making its debut this year on the women's side. Ledecky, 24, has broken 14 world records during her illustrious career.
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<strong>Nyjah Huston (United States):</strong> Skateboarding makes its Olympic debut in Tokyo, and Huston is one of the sport's icons. The 26-year-old, who has nearly 5 million followers on Instagram, has won three of the last four world titles in the street category. He's also won the most street medals in X Games history.
Nyjah Huston (United States): Skateboarding makes its Olympic debut in Tokyo, and Huston is one of the sport's icons. The 26-year-old, who has nearly 5 million followers on Instagram, has won three of the last four world titles in the street category. He's also won the most street medals in X Games history.
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<strong>Noah Lyles (United States):</strong> Lyles, center, is the current world champion in the 200 meters and many people's favorite to win the event at the Olympics, which Usain Bolt won in each of the past three Games. Bolt's retirement also opens the door for a new 100-meter champion. Lyles, 23, was expected to compete in that event, too, but he finished seventh at the US Olympic trials and failed to qualify. The winner of that race, Trayvon Bromell, is now among the favorites there.
Noah Lyles (United States): Lyles, center, is the current world champion in the 200 meters and many people's favorite to win the event at the Olympics, which Usain Bolt won in each of the past three Games. Bolt's retirement also opens the door for a new 100-meter champion. Lyles, 23, was expected to compete in that event, too, but he finished seventh at the US Olympic trials and failed to qualify. The winner of that race, Trayvon Bromell, is now among the favorites there.
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<strong>Stephanie Gilmore (Australia):</strong> Surfing makes its Olympic debut this year, and the highly decorated Gilmore will be one of the favorites on the women's side. The 33-year-old has won more world titles — seven — than any of her competitors. She'll be looking to beat out American Carissa Moore, the current world champ.
Stephanie Gilmore (Australia): Surfing makes its Olympic debut this year, and the highly decorated Gilmore will be one of the favorites on the women's side. The 33-year-old has won more world titles — seven — than any of her competitors. She'll be looking to beat out American Carissa Moore, the current world champ.
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<strong>Laurel Hubbard (New Zealand):</strong> Hubbard will be <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F06%2F21%2Faustralia%2Flaurel-hubbard-olympics-transgender-intl-hnk-spt%2Findex.html" target="_blank">the first transgender athlete to compete in the Olympics.</a> Hubbard, 43, competed in men's weightlifting competitions before transitioning in 2013. She has been eligible to compete in the Olympics since 2015, when the International Olympic Committee issued new guidelines that allow any transgender athlete to compete as a woman provided their testosterone levels are below 10 nanomoles per liter for at least 12 months before their first competition, according to Reuters.
Laurel Hubbard (New Zealand): Hubbard will be the first transgender athlete to compete in the Olympics. Hubbard, 43, competed in men's weightlifting competitions before transitioning in 2013. She has been eligible to compete in the Olympics since 2015, when the International Olympic Committee issued new guidelines that allow any transgender athlete to compete as a woman provided their testosterone levels are below 10 nanomoles per liter for at least 12 months before their first competition, according to Reuters.
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<strong>Allyson Felix (United States):</strong> Felix kisses her daughter, Camryn, at the US Olympic trials in June. Felix, 35, is the only female track-and-field athlete to win six Olympic gold medals, and she also has three silvers. If she wins a medal in Tokyo, she would stand alone as the most decorated female track star in Olympic history. Over the past few years, <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F06%2F19%2Fsport%2Fallyson-felix-road-to-tokyo-cmd-spt-intl%2Findex.html" target="_blank">Felix has been an advocate for change,</a> whether it be taking part in Black Lives Matter protests or standing up for maternal protections in contracts. This is her fifth Olympic Games.
Allyson Felix (United States): Felix kisses her daughter, Camryn, at the US Olympic trials in June. Felix, 35, is the only female track-and-field athlete to win six Olympic gold medals, and she also has three silvers. If she wins a medal in Tokyo, she would stand alone as the most decorated female track star in Olympic history. Over the past few years, Felix has been an advocate for change, whether it be taking part in Black Lives Matter protests or standing up for maternal protections in contracts. This is her fifth Olympic Games.
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<strong>Caeleb Dressel (United States):</strong> Michael Phelps, the most decorated Olympian of all time, has called it a career. But Dressel might be the next big thing in men's swimming. The 24-year-old has already got two Olympic gold medals, and he's the world-record holder in the 100-meter butterfly. He'll be racing in that event as well as the 50-meter freestyle and the 100-meter freestyle.
Caeleb Dressel (United States): Michael Phelps, the most decorated Olympian of all time, has called it a career. But Dressel might be the next big thing in men's swimming. The 24-year-old has already got two Olympic gold medals, and he's the world-record holder in the 100-meter butterfly. He'll be racing in that event as well as the 50-meter freestyle and the 100-meter freestyle.
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<strong>Janja Garnbret (Slovenia):</strong> Sport climbing is one of four sports making their Olympic debut this year, and Garnbret, 22, is <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F06%2F03%2Fsport%2Fjanja-garnbret-climbing-olympics-tokyo-cmd-spt-intl%2Findex.html" target="_blank">one of the best sport climbers on the planet.</a> The 2019 World Cup champion is heavily favored to win gold.
Janja Garnbret (Slovenia): Sport climbing is one of four sports making their Olympic debut this year, and Garnbret, 22, is one of the best sport climbers on the planet. The 2019 World Cup champion is heavily favored to win gold.
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<strong>Shi Tingmao (China):</strong> China's diving teams have been dominating Olympic competitions since 1984, taking home 40 gold medals out of a possible 56. Shi, 29, won two golds in 2016 and will look to add to that tally before calling it a career. She's owned the 3-meter springboard events since 2015, rarely losing an event.
Shi Tingmao (China): China's diving teams have been dominating Olympic competitions since 1984, taking home 40 gold medals out of a possible 56. Shi, 29, won two golds in 2016 and will look to add to that tally before calling it a career. She's owned the 3-meter springboard events since 2015, rarely losing an event.
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<strong>Sky Brown (Great Britain):</strong> The 13-year-old skateboarder lives up to her name, soaring through the air when she competes in the park event. Sky, Britain's youngest-ever summer Olympian, is ranked third in the world in park skateboarding. Her Olympic qualification finished an inspiring comeback story: Last year, <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2020%2F06%2F02%2Fsport%2Fsky-brown-injury-fall-skateboarding-spt-intl%2Findex.html" target="_blank">she fractured her skull and broke bones in her left hand</a> after falling from a ramp during training. Sky also was born in Japan. Her mother is Japanese and her father is British.
Sky Brown (Great Britain): The 13-year-old skateboarder lives up to her name, soaring through the air when she competes in the park event. Sky, Britain's youngest-ever summer Olympian, is ranked third in the world in park skateboarding. Her Olympic qualification finished an inspiring comeback story: Last year, she fractured her skull and broke bones in her left hand after falling from a ramp during training. Sky also was born in Japan. Her mother is Japanese and her father is British.
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<strong>Simone Manuel (United States):</strong> Manuel made history in 2016 when she became <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2016%2F08%2F12%2Fopinions%2Folympic-swimmer-simone-manuel-jones%2Findex.html" target="_blank">the first African American woman to win gold in an individual swimming event.</a> She won't be able to defend her crown in the 100-meter freestyle, as she wasn't able to qualify this time around, but she will be competing in the 50-meter freestyle. The 24-year-old also medaled in two relays in 2016.
Simone Manuel (United States): Manuel made history in 2016 when she became the first African American woman to win gold in an individual swimming event. She won't be able to defend her crown in the 100-meter freestyle, as she wasn't able to qualify this time around, but she will be competing in the 50-meter freestyle. The 24-year-old also medaled in two relays in 2016.
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<strong>Eliud Kipchoge (Kenya):</strong> Kipchoge, the only person to <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2019%2F10%2F12%2Fsport%2Feliud-kipchoge-marathon-vienna-intl%2Findex.html" target="_blank">complete a marathon in under two hours,</a> is a legend in the sport. The 36-year-old won Olympic gold in 2016 and is one of the favorites to win in Tokyo.
Eliud Kipchoge (Kenya): Kipchoge, the only person to complete a marathon in under two hours, is a legend in the sport. The 36-year-old won Olympic gold in 2016 and is one of the favorites to win in Tokyo.
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<strong>Hend Zaza (Syria):</strong> At 12 years old, Zaza is expected to be the youngest Olympian in Tokyo — and the fifth-youngest person ever to compete in the Olympics. The table-tennis player actually qualified in February 2020 when she was just 11. Because of the country's civil war, she hasn't been able to enter many tournaments, her coach has said.
Hend Zaza (Syria): At 12 years old, Zaza is expected to be the youngest Olympian in Tokyo — and the fifth-youngest person ever to compete in the Olympics. The table-tennis player actually qualified in February 2020 when she was just 11. Because of the country's civil war, she hasn't been able to enter many tournaments, her coach has said.
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<strong>Zhu Ting (China):</strong> Zhu is the captain of China's indoor volleyball team, which won Olympic gold five years ago in Rio de Janeiro. The 6-foot-6 outside hitter is 26 years old, but she's already considered one of the greatest volleyball players of all time.
Zhu Ting (China): Zhu is the captain of China's indoor volleyball team, which won Olympic gold five years ago in Rio de Janeiro. The 6-foot-6 outside hitter is 26 years old, but she's already considered one of the greatest volleyball players of all time.
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<strong>Shelly-Ann Fraser-Pryce (Jamaica):</strong> Fraser-Pryce, right, is looking to become the first woman to win the 100-meter dash at three different Olympics. The 5-foot-1 "Pocket Rocket" finished third in 2016 after winning gold in 2008 and 2012, but she rebounded <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2019%2F09%2F30%2Fsport%2Fdoha-world-championships-shelly-ann-fraser-pryce-spt-intl%2Findex.html" target="_blank">to win the event at the 2019 World Championships.</a> And in June, she clocked a time of 10.63 seconds, which is the second-fastest 100 time ever for a woman. If the 34-year-old wins gold in Tokyo, she would be the oldest person to win an individual Olympic sprint.
Shelly-Ann Fraser-Pryce (Jamaica): Fraser-Pryce, right, is looking to become the first woman to win the 100-meter dash at three different Olympics. The 5-foot-1 "Pocket Rocket" finished third in 2016 after winning gold in 2008 and 2012, but she rebounded to win the event at the 2019 World Championships. And in June, she clocked a time of 10.63 seconds, which is the second-fastest 100 time ever for a woman. If the 34-year-old wins gold in Tokyo, she would be the oldest person to win an individual Olympic sprint.
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<strong>Ryo Kiyuna (Japan):</strong> Kiyuna is from the island of Okinawa, which is considered the birthplace of karate, and he is one of the favorites to win gold as the sport appears at the Olympics for the first time. The 31-year-old competes in the kata event, which is a solo discipline where the athletes demonstrate various forms.
Ryo Kiyuna (Japan): Kiyuna is from the island of Okinawa, which is considered the birthplace of karate, and he is one of the favorites to win gold as the sport appears at the Olympics for the first time. The 31-year-old competes in the kata event, which is a solo discipline where the athletes demonstrate various forms.
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<strong>Kevin Durant (United States):</strong> Team USA has dominated men's basketball since 1992, when NBA players were first allowed to play and the "Dream Team" became a global phenomenon. The Americans have won the last three gold medals and six of the last seven — only coming up short in 2004. Durant, 32, is one of two returning players from the team that won in 2016, and he'll be looked to for leadership and scoring. Durant led the team in scoring in 2016, and he averaged 34.3 points in the NBA playoffs this year.
Kevin Durant (United States): Team USA has dominated men's basketball since 1992, when NBA players were first allowed to play and the "Dream Team" became a global phenomenon. The Americans have won the last three gold medals and six of the last seven — only coming up short in 2004. Durant, 32, is one of two returning players from the team that won in 2016, and he'll be looked to for leadership and scoring. Durant led the team in scoring in 2016, and he averaged 34.3 points in the NBA playoffs this year.
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<strong>Masahiro Tanaka (Japan):</strong> For the first time since 2008, baseball is back at the Olympics. Unfortunately, baseball-crazy Japan will not be able to cheer on the national team in person, as <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F07%2F08%2Fasia%2Fjapan-state-of-emergency-olympics-intl-hnk%2Findex.html" target="_blank">all Olympic spectators have been banned because of Covid-19.</a> Tanaka, a former New York Yankee who made two All-Star teams, now plays professionally in Japan with the Tohoku Rakuten Golden Eagles. The 32-year-old is one of the most well-known names on a team that includes pitcher Yoshinobu Yamamoto, shortstop Hayato Sakamato and outfielder Seiyka Suzuki. Major League Baseball players are not competing in Tokyo.
Masahiro Tanaka (Japan): For the first time since 2008, baseball is back at the Olympics. Unfortunately, baseball-crazy Japan will not be able to cheer on the national team in person, as all Olympic spectators have been banned because of Covid-19. Tanaka, a former New York Yankee who made two All-Star teams, now plays professionally in Japan with the Tohoku Rakuten Golden Eagles. The 32-year-old is one of the most well-known names on a team that includes pitcher Yoshinobu Yamamoto, shortstop Hayato Sakamato and outfielder Seiyka Suzuki. Major League Baseball players are not competing in Tokyo.
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<strong>Ariarne Titmus (Australia):</strong> The biggest threat to Katie Ledecky's dominance in the pool could be Titmus, a 20-year Australian nicknamed the "Terminator." Titmus defeated Ledecky in the 400-meter freestyle two years ago at the World Championships. Ledecky was battling a stomach virus at the time, but Titmus has only gotten better since then. She nearly broke Ledecky's 400-meter world record in June, finishing just .44 seconds off the pace.
Ariarne Titmus (Australia): The biggest threat to Katie Ledecky's dominance in the pool could be Titmus, a 20-year Australian nicknamed the "Terminator." Titmus defeated Ledecky in the 400-meter freestyle two years ago at the World Championships. Ledecky was battling a stomach virus at the time, but Titmus has only gotten better since then. She nearly broke Ledecky's 400-meter world record in June, finishing just .44 seconds off the pace.
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<strong>Megan Rapinoe (United States):</strong> The US women's soccer team is packed with superstars, including Rose Lavelle, Carli Lloyd and Alex Morgan. But it's impossible to take your eyes off Rapinoe, who scored the game-winning goal in the 2019 World Cup final and was named the tournament's best player. The 36-year-old has also been an <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F03%2F24%2Fpolitics%2Fmegan-rapinoe-equal-pay-day-congress-testimony%2Findex.html" target="_blank">outspoken advocate</a> for equality and inclusivity.
Megan Rapinoe (United States): The US women's soccer team is packed with superstars, including Rose Lavelle, Carli Lloyd and Alex Morgan. But it's impossible to take your eyes off Rapinoe, who scored the game-winning goal in the 2019 World Cup final and was named the tournament's best player. The 36-year-old has also been an outspoken advocate for equality and inclusivity.
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<strong>Karsten Warholm (Norway):</strong> Warholm <a href="index.php?page=&url=https%3A%2F%2Fwww.cnn.com%2F2021%2F07%2F02%2Fsport%2Fkarsten-warholm-breaks-world-record-spt-intl%2Findex.html" target="_blank">broke a 29-year-old world record this summer</a> when he finished the 400-meter hurdles in 46.70 seconds. It was the longest-standing record in men's track. Warholm, 25, has dominated the event over the last few years, winning the last two world titles.
Karsten Warholm (Norway): Warholm broke a 29-year-old world record this summer when he finished the 400-meter hurdles in 46.70 seconds. It was the longest-standing record in men's track. Warholm, 25, has dominated the event over the last few years, winning the last two world titles.
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<strong>Diana Taurasi and Sue Bird (United States):</strong> If the US women's basketball team wins gold — as it has in every Olympics since 1996 — then Taurasi, left, and Bird will become the first basketball players of any gender to win five Olympic gold medals. The two guards are two of the greatest women's basketball players of all time. Taurasi, 39, is the WNBA's all-time leading scorer. Bird, 40, is the league's all-time leader in assists.
Diana Taurasi and Sue Bird (United States): If the US women's basketball team wins gold — as it has in every Olympics since 1996 — then Taurasi, left, and Bird will become the first basketball players of any gender to win five Olympic gold medals. The two guards are two of the greatest women's basketball players of all time. Taurasi, 39, is the WNBA's all-time leading scorer. Bird, 40, is the league's all-time leader in assists.
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