LONDON –

Let's be honest, nothing Michael Phelps has accomplished as an Olympic swimmer should surprise us. Not after his perfect eight-for-eight gold medal quest in Beijing.

Twenty-one medals . . . and counting.

The Baltimore Bullet is a one-man Guinness Book of World Records.

Friday night's comeback for the ages, which produced his 17th gold medal, was truly amazing. Sitting in seventh place at the midway point of the 100-meter butterfly final, the two-time defending champion, made a comeback comparable to a baseball team rallying from nine runs down with two outs in the ninth inning. It was that improbable.

Or was it?

He makes the remarkable look routine.

Phelps has the perfect demeanor, competitive spirit and physique to vanquish all foes.

And he took the gold in 51.44 seconds at the Aquatics Centre, leaving South Africa's Chad le Clos and Russia's Evgeny Korotshkin, joint silver medalists (51.81), with a result they'll never forget.

After benefiting from the experience of competing for Team USA as a bright-eyed 15-year-old at the 2000 Sydney Olympics, where he was the youngest American male Olympian since 1932, Phelps' star has risen and risen and . . . traveled to another galaxy.

Phelps' third Olympic gold in the 100 fly was his final individual race. He has insisted he's retiring from competitive swimming. So what a brilliant — and fitting — conclusion to his race against, well, really himself.

The most decorated Olympian in history, Phelps will close out his career in the men's 4x100 medley relay on Saturday, He'll swim the butterfly leg for the United States.

Now's the appropriate time to consider what he's already accomplished, including a pair of unprecedented three-peats (100 fly and 200 individual medley) dating back to the 2004 Athens Games. It's time to be grateful that an athlete as exceptional and versatile has elevated the sport and inspired millions to swim at all competitive levels in every corner of the earth.

Michael Phelps has raised the bar so high that it seems impossible to think there will ever be another like him. (But if all this retirement talk is really nonsense, he may be back in the pool in Rio in 2016.)

Coach Bob Bowman, who has guided Phelps throughout his career, has seen the legend hold his own against the sport's elites competitors and watched the way the Phelps-Ryan Lochte rivalry has been a great story-within-the-story over the years.

That tale, too, is about to conclude.

"I think we will miss the races because they just showed us an incredible level of races," Bowman said. "They are two guys obviously very difference so it is kind of nice to look at those personality differences."

Phelps vs. Lochte, his American teammate, has been called the greatest individual rivalry in swimming history, and Bowman has developed a great sense of appreciation for what the two men have brought to the sport and how they have attracted a respectable following among even casual sports fans.

Bowman won't be barking orders at Phelps on a daily basis anymore. Which means he can store all the details in his brain for future book deal or a movie — or what the heck, he can just savor the memories.

"I am definitely going to miss it," the coach said, "but by the same token, we've had a really good run. We will take it."

Under Bowman's tutelage, Phelps has collected 21 medals, while in London he missed out on a 400 IM medal by placing fourth — a rare glimpse of being an actual human in the pool. (A medal in the 4x100 medley relay Saturday night would give him six medals in seven London races.)

"You can see what Michael did (here in London) was fantastic, and it's still not quite Beijing," U.S. coach Gregg Troy said after Phelps earned his 20th medal on Thursday.

Missy Franklin, the 17-year-old darling of American swimming, has collected four medals in London, including three gold, and considers Phelps an important role model for her, the ideal mentor for how she approaches swimming.

"He's helped people to think the impossible," Franklin told reporters. "It's made us push what we can do."

In my view, Phelps has enjoyed the overall experience here in London more than in Beijing. Simply put, he has looked happier and walked around with a more relaxed, easygoing vibe.

Yes, he takes his sport very seriously, but he has loosened up and his body language and interaction with teammates, the media and fans here in England show a man having, well, more fun here.

Speaking after the 100 fly triumph, Phelps said, "I'm just happy that the last one was a win. That's all I really wanted coming into the night."

When he departs London, the full realization of what he accomplished here and in past Summer Games will sink in, But, as expected, it's too early for that.

"I guess a lot of those emotions haven't really come through my brain over the last week," he told reporters, trying to offer an explanation about what he's thinking and feeling on the eve of retirement. "Once I'm done and once tomorrow is over, I think there's going to be a lot more emotion that really comes out."

In the future, Phelps plans to spend a lot of time on the golf course. He said he'll avoid spending countless hours in the pool. Furthermore, as he told ESPN.com's Rick Reilly, a comeback in a few years is out of the question.

"Me? At 30? Swimming?" Phelps was quoted as saying in the Reilly column, published in May. "Oh, no. Oh, God, no! At 30, I'll be playing golf every day."

Bowman, his longtime coach, piqued his interest in golf.

"I want to play all the great (golf) courses," Phelps told Reilly. "(Bowman) gave me a poster with the 100 greatest courses in the world on it, and every time I play one, I put a little pin in it."

In that May column, it was reported that Phelps hadn't yet played one of those hundred golf courses.

After what he's accomplished over the past three Olympiads, I imagine he'll be given VIP treatment at any country club in the world. How's that for an encore?