Michael Phelps and Usain Bolt -- who have earned 28 Olympic medals between them, while reaping millions in endorsement deals -- have confirmed that Rio 2016 will be their last Olympic runs.
American swimmer Phelps has won 18 golds, double the next biggest haul in history, while Jamaican sprinter Bolt, has run two Olympic sweeps in the 100m, 200m and 4x100m relay. Unless a miracle can preserve the bodies of these once-in-a-generation athletes, a gaping hole in Olympic sponsorship deals will need filling at future games.
Looking through the line-up, it's hard to pick out one individual on the cusp of the kind of world fame enjoyed by Phelps, and especially Bolt, who was quick to flash his Hollywood smile and thunderbolt stance after winning each of his six golds.
Bolt earned an estimated $30 million
last year from endorsement deals alone, and Phelps' annual endorsement haul is an estimated $10 million.
An informal poll of journalists covering the Games did not yield any obvious candidates, but then, both the Jamaican and the American failed to grab many headlines (by their standards) at their first Olympics.
At the Sydney 2000 Games, 15-year-old Phelps was the youngest US Olympic swimmer for almost 70 years -- but finished outside the medals in his one event, the 200m butterfly. In 2004, 17-year-old Bolt went out in the first round of his only event, the 200m.
With that in mind, a future Phelps or Bolt might make only a small impression this time around.
Here is a selection of candidates for whom Rio could be their launching pad, and one or two whose Olympic superstardom may be some years off.
Katie Ledecky, age 19, USA
Ledecky is almost guaranteed to be the closest thing to a Phelps -- except Phelps himself -- at the Rio Games.
She has recently dominated U.S. women's swimming, amassing world records over the 400m, 800m and the non-Olympic 1500m freestyles. At last year's world championships, Ledecky won every freestyle event from the 200m to the 1500m and starred in the gold medal-winning US 4x200m freestyle relay team.
Ledecky has already been to the Olympics once, as a 15-year-old who upset Britain's Rebecca Adlington to win 800m freestyle gold at the London Olympics. Four years later, she is still the youngest U.S. swimmer on the plane to Rio.
The Maryland teenager will start as the favorite in each of her three individual events -- some way short of the five individual titles Phelps won at Beijing 2008, but still certain to be one of Rio 2016's lasting storylines if it comes to pass. No woman has pulled off Ledecky's anticipated 200m, 400m and 800m freestyle triple-play since 1968.
However, it remains to be seen if that kind of success in Rio could earn Ledecky the household-name status and commercial value attached to Phelps. So far, despite nine world gold medals in two outings, that hasn't materialized.
Caeleb Dressel, 19, USA
Dressel, who turns 20 at the Rio Games, could be this year's breakout male on the U.S. swim team.
Dressel is a straight-up sprint swimmer, although lacking in Phelps' diverse range of events in which to win medals. He is, however, earning comparisons to another all-time U.S. great: Ryan Lochte.
Lochte, 31, has five Olympic titles from three Games and could add more in Rio; Dressel will get two bites at an Olympic medal, in the men's 100m freestyle and 4x100m freestyle relay.
The hype around Dressel comes despite an improbable two-year hiatus as a 17-year-old. "I was just trying to figure some things out spiritually. I wanted swimming to be something that I loved, something that I was motivated to do for myself," he told Sports Illustrated. "I guess you could say it was a walk in the wilderness."
Dressel returned from that walk in style, setting national records over both 50-yard and 100-yard freestyles while representing the University of Florida at this year's NCAA championships, His coach Gregg Troy insists his "perfect race" is still to come.
Simone Biles, 19, USA
The Columbus, Ohio native will command more screen time than most in Rio. The world loves its gymnastics and Biles has been the undisputed queen of the sport since London 2012, amassing 10 world titles in three years.
In Rio, Biles is far and away the favorite for the individual all-around title, and is also expected to lead Team USA to a group medal. Given that Biles won four golds at the world championships in 2015, winning four or more golds in Rio is by no means out of the question.
It is rare, however, for a female gymnast to star at the very top for more than one Olympics. In fact, pulling a Phelps or Bolt and challenging for the highest honors for over multiple games is practically unheard of in gymnastics.
Uzbekistan's Oksana Chusovitina, for example, will make it into every Rio "oddball" list as this is her seventh Olympics. At 41, she will be more than a decade older than almost every rival. But Chusovitina, in six appearances to date, has just one gold and one silver to her name.
Ordinarily, observers would expect Biles to blitz the medals in Rio and then fade away like her compatriots Mary Lou Retton (five medals in Los Angeles 1984) and Kerri Strug (one memorable gold in Atlanta 1996 and a bronze in Barcelona 1992), but competing in Tokyo 2020 is not impossible. In fact, two Americans returning from London 2012 -- double champions Aly Raisman and Gabby Douglas -- will be back for Rio, proving it can be done.
Trayvon Bromell, 21, USA
Historically, the U.S. has dominated the 100m sprint, but has been largely been forgotten as a threat in the event. No American has finished higher than third since Justin Gatlin won gold back in 2004 (and he then succumbed to an eight-year ban), but Team USA thinks it has the next big thing with Trayvon Bromell.
Bromell, who turned 21 earlier in July, has been living with the "next Bolt" tag for at least a year since running to 100m bronze behind Bolt and Gatlin at 2015's world championships in Beijing.
He has since added the world indoor 60m title to his resumé, and was second in U.S. Olympic trials behind Gatlin.
Bromell shares an agent with Usain Bolt, although the two don't share many other similarities: Bromell, for example, is 5-foot 9-inches to Bolt's 6-foot 5-inches.
"I said in the third grade that I wanted to be an Olympian and people laughed at me," Bromell told The Oregonian earlier this year. "Now I'm here."
Yohan Blake, 26, Jamaica
Remember him? Yohan Blake was the 100m and 200m silver medalist at London 2012 behind teammate Bolt, but has since endured four trying years punctuated by hamstring injuries.
Blake is now 26, and if the man once tipped as Bolt's successor -- who shares the second-fastest ever 100m time -- is going to recapture that tag, Rio is the place to do it.
He won both the 100m and 200m in Bolt's injury-related absence at Jamaica's Olympic trials, but was warned by coach Glen Mills -- who also trains Bolt -- that he needs to up his game substantially to be a threat in Rio.
Blake, for example, won the 200m trial in a modest 20.22 seconds, while Bolt has spent the year threatening rivals with his ambition of running the Rio final in under 19 seconds.
For his part, Blake says he is finally injury-free and closing in on the world's fastest times. But if he strikes gold in Rio, don't expect his trademark "Beast" celebration: He told reporters in April that he wants to shed the nickname for the rest of his career.
Bronte and Cate Campbell, 22 and 24, Australia
Part of Bolt and Phelps' appeal over past Games is that their triumphs came with storylines: In Phelps' case, a return from a drunken driving incident and a suspension for smoking pot; in Bolt's case, avenging a second-place finish at Jamaica's qualifying trials in the lead-up to London.
Australia's Campbell sisters may bring that to the table. Cate and Bronte are leading the national swim team's efforts to redeem itself after an underwhelming London 2012, where neither qualified for the 50m freestyle final.
Both sisters say they are driven to succeed in part on behalf of younger brother Hamish, who has cerebral palsy.
Cate Campbell set the women's 100m freestyle world record at the start of July, but Bronte is the reigning world champion. Both Campbells, meanwhile, swam in the Australian team that won the 4x100m freestyle relay world title. Between them, they could be taking home six golds from Rio.
Sarah Menezes, 26, Brazil
If the host country is going to supply a global breakthrough at Rio 2016, it could be Sarah Menezes in judo.
Menezes won gold at London 2012, and is one of Brazil's strongest hopes for gold next month. When she carried the Olympic torch during its journey to Rio, crowds lining the streets showed their level of expectation by chanting for her to win a second gold medal this summer.
With her event, the 48 kg judo weight class, held on the first day of the Games, she could achieve national stardom early by becoming Brazil's first Olympic champion on home soil.
A more realistic global name from the Brazilian ranks in Rio is Neymar.
Capped more than 70 times by Brazil's national football team, the 24-year-old Barcelona star is one of three "over-age" players (above the age of 23) allowed in the Brazil under-23 side for Rio's Olympic football tournament.
Neymar's fame comes from Spanish football, but leading the hosts to glory in Rio would see his legacy cemented back home -- and enhanced as a pitchman globally.
Tom Daley may be Britain's biggest celebrity athlete heading to Rio. The diver has amassed millions of fans since making his Olympic debut as a 14-year-old in 2008, going on to win bronze in front of home fans in London four years later.
It remains to be sen whether a 10m platform victory in Rio -- which is certainly within grasp -- will give Daley, now 22, a broader profile as a face of the global Games.
Japanese gymnast Kohei Uchimura has arguably achieved as much in his sport as Phelps and Bolt have in theirs. Despite only one Olympic title to his name, Uchimura has been dominant at world level since 2009 and is widely considered the greatest-ever male gymnast.
Though he plans to hang on for his home Games in Tokyo if he can, Uchimura admits he will be in the twilight of his career after Rio. Moreover, the 27-year-old cuts a shy character in public and has rarely exploited his stardom.
American Missy Franklin was, for a time, earmarked to succeed Phelps as swimming's conqueror of all comers -- not least because the 6-foot 2-inch, 17-year-old won four Olympic titles on her debut in London.
Although Franklin went on to win six world titles a year later, she has been plagued by injuries since and will operate away from Ledecky's spotlight in Rio.
Lastly, keep an eye on Sydney McLaughlin, representing the U.S. in the women's 400m hurdles.
McLaughlin, 16, looks like she may be developing into one of America's brightest female track prospects in years. Only four of her Rio rivals have run the event faster than McLaughlin in 2016, while teammate and four-time Olympic champion Allyson Felix has already flagged her as a talent to watch.
McLaughlin could even have a chance at a medal if she keeps her head straight as one of the youngest members of Team USA in Brazil: She turns 17 on August 7, just a week away from her Olympic track and field debut.