WHERE ARE THEY NOW? The stars of the 2016 Rio Olympics

Michael Phelps led all Olympians with six medals, five of which were gold.

Phelps has since retired as the most decorated Olympian ever. He is now a mental health advocate.

Simone Biles became the greatest gymnast ever at Rio in 2016, taking home five medals, including four golds.

Biles is back for Tokyo. She's better than ever and looking to further cement her greatness.

Katie Ledecky had her breakout, finishing with five medals, four of which were gold.

Ledecky returns to the pool in Tokyo, where she'll be a favorite to take home more golds.

Usain Bolt wowed in Rio, winning three gold medals and making it look easy in the process.

Bolt is retired, but still staying in shape on the track. He also briefly tried his hand at soccer.

Read more: Usain Bolt says a bet with friends that he'll 'get fat' motivates him to keep working out in retirement

Aly Raisman won a gold and two silvers in gymnastics in Rio.

Raisman is no longer competing, but she has taken a lead role in calling for transparency from USA Gymnastics after coming out as a survivor of Larry Nassar's abuse. She has also become an advocate for other survivors of assault.

Simone Manuel also broke out with a gold medal in the 100-meter freestyle in an upset victory.

Manuel will be in Tokyo, serving as a captain of the swim team while also competing in the 50-meter freestyle.

Not everyone who was a star at Rio was a medal-winner. Pita Taufatofua of Tonga made waves with his shirtless, oily body at the opening ceremony.

Taufatofua went on to make the Pyeongchang Olympics as a cross-country skier, and he will be back in Tokyo competing in taekwondo.

Robel Kiros Habte of Ethiopia became a fan-favorite for his physique and last-place finish in the 100 freestyle. Although he said he wanted to compete in Tokyo, according to FINA's website, he hasn't competed since Rio.

Ryan Lochte didn't win any medals at Rio but made headlines for his bleached hair and for his robbery scandal.

Lochte admitted to struggling with mental health after Rio and also went to rehab for alcohol. Lochte attempted to make a comeback for the Tokyo Olympics but fell short of qualifying.

Lilly King became a breakout star for taking on Russian rival Yuliya Yefimova, who had served a doping suspension, and won. King won two medals.

King will be in Tokyo, attempting to become the first woman to win the 100-meter breaststroke in back-to-back Olympics.

Laurie Hernandez took home a gold in the team event and a silver in the balance beam.

Hernandez took a break from gymnastics after the Olympics. She tried but did not make team for Tokyo.

Joseph Schooling of Singapore became a breakout star when he beat his idol Michael Phelps in the 100-meter butterfly.

Schooling will be in Tokyo to compete for gold again in the same event.

Justin Rose took home gold in the golf event.

Rose is ranked 47th in the world but missed the cut for Tokyo.

Kerri Walsh-Jennings and April Ross took home the bronze medal in beach volleyball in Rio.

Walsh-Jennings failed to qualify for Tokyo while playing with a new partner in Brooke Sweat. Ross, meanwhile, qualified with a new partner in Alix Klineman.

Japanese gymnast Kohei Uchimura won gold medals in the team event and all-around.

Uchimura is widely regarded as the greatest male gymnast ever. He qualified for Tokyo in the individual high bar for what is likely his last Olympics.

Allyson Felix won three medals, including two golds in relays, in Rio.

Felix, who had to undergo an emergency C-section at just 32 weeks pregnant in 2018, qualified for Tokyo in the 400 meters.

Katinka Hosszu of Hungary won four medals, the most of any non-American, and her husband gained notoriety for his enthusiastic celebrations.

Hosszu is heading to Tokyo, set to compete in four events.

Caeleb Dressel won two gold medals in relays.

Dressel has since dominated world championships in 2017 and 2019 and will be swimming in six or seven events in Tokyo.

Now, check out some athletic duos who will be in Tokyo...

9 Olympic couples competing together at the Tokyo Olympics >