Michael Phelps is the most decorated Olympian of all time. But is that the same as being the 'greatest'?
That was the question left hanging in the air after the swimming superstar won the 19th Olympic medal of his career by anchoring the US 4x200m freestyle relay team to gold in London on Tuesday.
That saw him overhaul the record of 18 medals amassed by Soviet gymnast Larisa Latynina between 1956 and 1964.
Phelps's haul, which includes 15 golds, is outstanding.
But swimmming opens itself up to producing multiple-medal winners by having categories for styles as well as distances.
So while athletics has the 100m, in swimming the distance can be covered in several different ways.
And there are those who argue longevity is a key factor in determining greatness - Phelps is still only 27 and his medals have been amassed over the space of just three Games.
However, longevity wasn't an option for Jesse Owens, who overcame barriers of racial prejudice to win four track and field golds in Berlin in 1936 and was then stripped of his amateur status for accepting a few commercial offers.
And even if he had still to be allowed to compete Owens, like many contemporaries, would have seen his career cut short by the Second World War when the Games were suspended.
That Phelps could even contemplate winning eight gold medals at a single Games, as he did four years ago in Beijing, was in a sense only possible because fellow US pool great Mark Spitz had won a then record seven - and all in world record times - at Munich in 1972.
That feat redefined the scope of Olympic achievement, with every subsequent multi-medallist sympathising with Spitz's remarks, just before he won his seventh gold, when he said: "If I swim six and win six, I'll be a hero. If I swim seven and win six, I'll be a failure."
Swimming is also one of the showpiece sports of the Games and that, along with modern mass commuications, has heightened Phelps's profile.
By contrast Germany's Birgit Fischer has received nothing like the same publicity for winning eight canoeing golds over six Olympics, despite missing the 1984 Games because of the then East Germany's political boycott.
Steve Redgrave, widely regarded as Britain's greatest Olympian after winning five gold medals, one at each games from 1984 in Los Angeles to Sydney in 2000, is well-placed to consider Phelps's standing.
"He has been able to pursue multiple golds at his last three Olympic Games, and one might argue that this diminishes his place among the greats. But how do you rank greatness?," Redgrave wrote in Wednesday's Daily Telegraph.
"With 15 gold medals he already has to be listed as one of the finest Olympic athletes ever, and yet I still believe his feat would have been more impressive if he achieved it over six or seven Games."
There are those who maintain the decathlon remains the ultimate test of Olympic excellence and that a gold medal winner should thus be considered the athlete of the Games.
So how much greater does that, say, make Britain's Daley Thompson, who won decathlon gold at both the 1980 Games in Moscow and again in Los Angeles?
For Redgrave, who denied, against a backdrop of a running public spat between the two men, that he had a "rift" with Thompson, the answer is clear.
"It is extremely impressive to be able to do that (the decathlon), but your rivals are not specialists - they are generalists, just like you.
"You are never going to be competing against Usain Bolt in the 100 metres, or against Liu Xiang in the high hurdles."
In the end the question of who is the greatest is one where a defintive answer often proves elusive, a point London 2012 chairman Sebastian Coe, himself twice a track 1500m gold medallist, summed up on Wednesday.
"This is the global pub game - who is the greatest Olympic athlete of all time?" said Coe.
"You have to say he (Phelps) is up there, but whether he is the greatest? In my opinion, probably not. But my opinion is no different from anyone else."