Phelps, the phenomenon: Phelps during the 4x100m medley relay, which gave him his eighth gold in the Beijing Olympics. (AFP)

The deed was done. He was done. The sense of completion was total as Michael Phelps drove an arm in the air, amid a roar that sounded like a giant exhalation from the crowd on Sunday at the Water Cube. His unprecedented eighth gold medal, which came on a lashing collective effort from the US men’s 4x100-metre medley relay team, was the greatest individual triumph in Olympic history, and there was simply nothing more to win.

“Everything was accomplished,” he said. “What else could I do?”

The Americans were in third place and the gold was in doubt when Phelps plunged into the water at the midway point for his butterfly leg. But with one last turn, massive dolphin kick and torso-heaving effort, Phelps glided into first place, and freestyler Jason Lezak brought home the victory and yet another world record, 3 minutes 29.34 seconds.

The men joined in a water-slick embrace, and then Phelps stood alone and unfolded those extraordinarily long arms toward the thundering rafters. He had gone one better than Mark Spitz, whose record of seven gold medals in one Olympics had stood since 1972, and he had done so with every brand of victory conceivable, swimming his personal best in every single race.

“It’s been such an unbelievable roller coaster,” he said. “It’s been such an unbelievable ride.”

For the last time at this meet, his 17th race in nine days, Phelps had ambled on to the white-tiled pool deck in that knee-length overcoat, something a gunfighter would wear. He once more went through his pre-swim routine, wiping the starting block with his towel, shucking the coat to reveal the leggings that looked so oddly Victorian, and shaking out those jointless limbs.

If he was conscious of the crowd, he didn’t show it. He simply stared ahead at the glittering aquamarine water. Phelps had swum with such dogmatic concentration throughout the meet that it was odd to hear him call his feat an act of “imagination”. Still, that’s what it was.

Phelps did not seem ambitious in any ordinary sense. He never seemed interested in becoming the all-time Olympic champion to revel in the celebrity of it. He competed less against others than against some faint abstract outline of the possible. In fact, he seemed acutely isolated, a man with a distant stare and a heart made like a timepiece, executing perfectly aligned strokes with invariable precision, and a seemingly tactile sense of the ticking seconds.

But the greater his success in controlling himself and events, the more he seemed to prize the unexpected, and the unintentional. The races in which he was most domineering seemed to leave him almost flat, as if he had merely done what he was supposed to. His most demonstrative moments — and emotionally satisfying — came when he was most anxious and jeopardised.

In the 100-metre butterfly on Saturday, he turned the challenging words of Milorad Cavic, who said he would like to be the guy to ruin Phelps’s Olympics, into a dull, submerged fury. After he out-touched Cavic by a hundredth of a second, he beat the water into great geysers of triumph. He then swivelled his head momentarily to stare at the Serb. “Nice swim,” he said curtly, and turned his back.

Ultimate verification of the breadth of Phelps’s performance was the fact that his victory over Cavic was just one of at least four moments that will endure as among the greatest in swimming history.

There was his world record in the muscle-searing 400 individual medley to open the meet. There was his scream, a cry of the soul, as the Americans came from behind to win the 4x100 freestyle relay, thanks to Lezak’s gutty closing leg. There was his dash to victory in the 200 butterfly with a world record despite goggles full of water.

What will Phelps imagine next? London looms. In four years, Phelps will be just 27, still very much in his prime. With 14 gold medals already, 20 is conceivable.

What kind of champion will Phelps evolve into? Eight years ago in Sydney, he was a thin-chested 15-year-old, finishing fifth in the 200 butterfly. “Who’s this Mark Spitz and why does everybody keep asking me about him?” he asked coach Bob Bowman. Four years ago, he was a 19-year-old squid boy as he won six golds.

In his place, here was a fully mature and peaking champion, both physically elastic and mentally unassailable. Facing 17 races over nine days, he actually remarked before the meet began that he wished it lasted even longer. “I’m going to swim my heart out,” he said.

He hasn’t found the bottom of it yet.

THE GREATEST?

Is US swimmer Michael Phelps the greatest ever Olympian?
Here’s a comparison with possible contenders

Michael Phelps

Most Olympic golds (14), five more than anyone else, including US swimmer Mark Spitz
Most golds at a single Games (8), one more than Spitz in Munich 1972

BUT

Swimming more forgiving on body than track or gymnastics, and high number of closely related events makes it easier to win multiple medals

Hasn’t a long-term record yet, having won at two Olympics

THOSE WHO HAD IT TOUGHER

Carl Lewis (US)

Nine golds, including four in Los Angeles 1984. Few have been as good both at sprints and long jump. Four straight golds in long jump (1984-96) prove longevity

Paavo Nurmi (Finland)

Nine golds in 1,500m to 10,000m over three Olympics (1920-28) before being ruled out for no longer being an amateur

Larissa Latynina (Russia)

Nine gymnastics golds, 18 total medals (highest) over three Olympics (1956-64)

AGELESS WONDERS

Birgit Fisher (Germany): Eight kayaking golds in six Games spanning seven Olympics (1980-2004). In Athens, she won gold as a 42-year-old mother of two

Aladár Gerevich (Hungary): Six fencing golds in six straight Olympics despite two passed over because of World War II. For the 28 years from 1932 till 1960, the world had just one champion in Olympic sabre

FOR HEROISM

Jesse Owens (US) Rose above a life of racial discrimination to become first track and fields athlete to win four golds at a single Games (Berlin 1936), shattering Hitler’s theory of Aryan supremacy