Twin titans Usain Bolt and Michael Phelps have mined a trove of Olympic gold, changed the sporting landscape and left a huge hole that starts in Rio and goes around the world.
International Olympic Committee president Thomas Bach hailed the two superstars as "icons". But he will leave the 31st Olympic Games wondering how to fill their places.
There is noone in sight with the sporting power nor the charisma to take the place of Phelps and Bolt -- who have 32 gold medals between them -- in the swimming pool or on the running track.
"The Greatest" maybe just Muhammad Ali-style hyperbole that Bolt likes to throw about but his nine golds over three Olympics cannot be countered.
Phelps won five golds in Rio at the age of 31 having retired once and come back -- and crashed a car under the influence along the way.
"We have seen athletes who were icons even before they arrived here, they have strengthened their position as icons, like Michael Phelps and Usain Bolt," Bach said Saturday.
From Beijing in 2008 through London 2012 and, finally, in Rio, Bolt and Phelps captivated die-hard fans of their sports and casual spectators attracted like moths to the Olympic flame.
Both presaged their mature exploits with precocious Olympics appearances, Phelps as a 15-year-old contesting the 200m butterfly in 2000, and Bolt, at 17, finishing fifth in his heat in the 200m in 2004.
By those Games in Athens in 2004, Phelps was already challenging Mark Spitz's record of seven titles at one Games, coming away with six golds and two bronze.
In Beijing he cemented his place among Games greats with a perfect eight golds in eight events at the Water Cube while Bolt electrified the Birds' Nest stadium with his 100m, 200m and 4x100m sprint triumphs.
From Beijing on they were linked in Games lore, each adding to his legacy in 2012 -- Bolt with another sprint sweep and Phelps with four more gold to add to his staggering tally of Olympic medals.
Although a burned-out Phelps flirted with retirement after London, it was fitting that his decision to return for one last, fifth, campaign, saw him bow out at the same time as Bolt. The Jamaican's unprecedented third sweep of the 100m, 200m and 4x100m means debate will rage loud and long as to which can claim the status of "greatest Olympian".
Phelps leads the medals table by a mile. His five golds in Rio took his already stunning tally to 23 gold among a total of 28.
Bolt, meanwhile, has dominated in the tests of speed that are the quintessential sporting contests, maintaining his supremacy over an unprecedented span of years.
"I've proven to the world I'm the greatest," declared the ebulliant Jamaican, who preens and poses with the same unabashed ardor with which he runs.
"It's a massive gap, but it's not a gap that is insuperable," International Association of Athletics Federations president Sebastian Coe said of Bolt's departure.
He compared it to questions asked with Ali's withdrawal in the 1970s. "Well, Floyd Mayweather, Marvin Hagler, Manny Pacquiao and Sugar Ray Leonard come along."
Bolt's bouncy showmanship -- complete with sly grins for out-classed rivals as he passes them with the finish line in sight -- is the opposite of Phelps's steely competitive demeanour.
But the American revelled in his Rio triumphs, and showed a softer side with infant son Boomer included in his victory celebrations.
"As a kid I set out to do someting that nobody had ever done before," Phelps said. "I can look back at my career and say: 'I did it.'"
Bolt, now headed into a year-long victory lap that will culminate with the World Championships in London, can say the same.
"I'll have to make a new bucket list now," Bolt said. "I've achieved all I wanted to in track and field."
Bolt has a wealth of riches to carry out his wishes.