By Steve Keating

RIO DE JANEIRO (Reuters) - Michael Phelps left the Olympic pool for the last time on Saturday having fulfilled a childhood dream, but it is clear he will not be walking away from the sport that has turned him into a global household name.

Phelps' swimming career ended with his 23rd gold medal in the 4x100 medley relay medal on Saturday, which extended his record as the most decorated Olympian of all-time.

"This all started and began with one little dream as a kid that changed the sport of swimming and tried to do something nobody else has ever done," said Phelps. "And it turned out pretty cool."

It could have all ended four years ago, a little less cool, for the now 31-year-old American.

After the 2012 London Olympics, which he had declared to be his last, Phelps walked away with not only the regret that he simply went through the motions but like many athletes in retirement, he appeared lost and unprepared.

He talked of becoming a professional golfer but eventually found himself testing the waters of a swimming comeback and despite some missteps with a drink driving conviction that led to rehab and a suspension, made his fifth Olympic team.

In Rio, where he took his Olympic tally to a staggering 28 medals -- he also won three silvers and two bronze -- it was apparent he was not going through the motions at all.

Clearly exhausted, he shared every victory with the raucous crowd and was especially emotional whenever he caught sight of fiancée Nicole and infant son Boomer in the stands.

"Getting off the bus walking into the pool tonight I almost felt myself starting to cry," said Phelps.

"Last warmup, last time putting on a suit, last time walking out in front of thousands of people representing my country it's insane.

"A lot better than it was four years ago, this is how I wanted to finish my career. This was the cherry on top of the cake and looking forward to starting a new chapter."

GOING MAINSTREAM

Part of that new chapter, having stated numerous times he would not be competing in Tokyo in 2020, now clearly lies outside the pool.

Since he first took the Olympic plunge at the 2000 Sydney Games he has had an ambition to take swimming into the mainstream and there is no doubt the sport has enjoyed a much higher profile during his tenure as its leading figure.

It is also apparent, however, he has not been able to elevate it much beyond what it has been - something people only care about during Olympic years and he knows he has work to do.

"I've said this to some of you, it's not done growing," he told reporters when he qualified for Rio. "In my opinion, and if I have to die before -- I'll go down swinging to see this sport where I want it to be.

"It's not done yet; it's not done growing, not in the U.S., and I'm going to continue to try to do it.

"I said when I was 15 years old, I want to change the sport of swimming. Yeah, I've done a lot, but it's not done."

While he does not have to put himself through the daily grind of training, it seems almost certain that Phelps' next career involves continuing to try to boost the sport's profile.

"Michael may not be competing anymore but he is still going to be very involved in the sport," said team mate Ryan Murphy.

"He started his own swim line, I think he is going to continue to try to grow that, there's not going to be an event he's not going to be at.

"Maybe he will get into commentating, maybe he will find some other business venture he can get involved in but he's not going to be out of the sport."

(Editing by Greg Stutchbury)