As a professional boxer who has plied his trade for 17 dominant years, and earned pyramid-high stacks of cash in the process, Floyd Mayweather Jr. has not had to swallow the sour taste of defeat. He is 43-0, with 26 knockouts, and aside from a few momentary hiccups , never has been seriously threatened during all that time. Even at the relatively advanced age of 36, “Money” is so confident that his oh won’t ever go that he has proclaimed himself high above the vaguest hint of failure. How could the most flawless fighter ever to lace up a pair of gloves (and if you don’t believe that, he’ll be glad to tell you again) be taken down by a mortal man? Would the mighty gods of Greek mythology atop Mount Olympus fear someone on Earth hewn of flesh and bone?

Mayweather, who puts his WBC welterweight championship on the line Saturday night against Robert Guerrero (31-1-1, 18 KOs) in a Showtime Pay-Per-View bout at Las Vegas’ MGM Grand, considers the possibility that he might not be invincible to be as ridiculous as Dr. Sheldon Cooper, the resident know-it-all on The Big Bang Theory, might the suggestion that he isn’t always the smartest guy in the room.

“Of course I feel unbeatable,” Mayweather replied to a teleconference question regarding his own towering sense of self-worth. “I’m the best. I’m not going into any fight figuring that I’m beatable. Anything is possible in life, but as far as my career, I feel I can adapt to anything.”

Ask Mayweather how he would stack up, prime on prime, with the most gifted and charismatic fighters of all time in and around his weight class – Sugar Ray Robinson, Sugar Ray Leonard, Roberto Duran, pick a legend, any legend – and the Grand Rapids, Mich., native always envisions having his hand raised in triumph. He is not so much about getting past Guerrero – or any potential victim, if he actually does fulfill the six-bouts-in-30-months terms of his contract with Showtime/CBS that conceivably could pay him up to $250 million – as he is about adding ever-higher and more ostentatious levels to the monument to himself he continues to construct.

“I want to make a legacy for myself as the greatest fighter who ever entered the ring,” he said. “Being a legend, wanting your name mentioned in the mix of other (great) fighters’ names, that’s why I work so hard right now. I’ve been fighting since 1987. I’ve been a professional for 17 years, and I’ve been dedicated to my craft.

“Last time I checked, I was 43 and 0. I’m not going to be impressed by no opponent. I’m going to go out and do what I do best, which is to always beat the opponent that’s in front of me.”

But, if you go back far enough into Mayweather’s past, it’s reasonable to assume he is as susceptible to disappointment inside the ropes as anyone else. Guerrero might hold the winning numbers to the megabucks lottery in which all of Mayweather’s wannabe dance partners are intent on playing, although it does seem a longshot proposition. A few years ago, the Powerball jackpot might or might not have gone to Manny Pacquiao, although that’s something we aren’t likely to know for sure since that superfight’s expiration date seems to have passed forever. Maybe the most dangerous future test for Floyd – the guy now cast as the Pac-Man equivalent – is WBC/WBA 154-pound champ Canelo Alvarez. We’ll just have to wait and see how Mayweather’s end game works out before offering any final judgments.

But let the record show that Floyd Jr. – just 10 when he was introduced to the family sport (Floyd Sr., who now trains his son, took Leonard into the 10^th and final round before being stopped in 1978, and uncle Roger was a two-division world champion) – was 84-6 as a celebrated amateur, winning three national Golden Gloves titles and a berth on the 1996 U.S. Olympic boxing team that competed in Atlanta.

Several of those six amateur setbacks came when Floyd was a kid, still mastering the myriad nuances of boxing. But even when his undeniable skills were almost fully developed, the last of those slaps to his sensibilities came at the Olympics, which should serve as a reminder that any fight that goes to a decision, be it amateur or professional, can end with the scales of justice tipped crazily to the wrong side. Ask Roy Jones Jr. about what happened in his gold-medal bout against South Korean punching bag Park Si-Hun in the 1988 Seoul Olympics. Ask any number of pro superstars who did everything seemingly necessary to win only to be stunned when the official scorecards were announced. Big reputations are generally a plus for a fighter, but they do not offer total protection from malfeasance by pencil.

For 19-year-old Floyd Mayweather Jr., the myth of his own invincibility was shattered, if it hadn’t already been by his five previous stumbles, in the Olympic semifinals. Touted by U.S. Olympic coach Al Mitchell as the best defensive fighter on the team, and not bad on offense either, he had defeated Kazakhstan’s Bakhtiyar Tileganov (by RSC-2, the equivalent of a technical knockout), Armenia’s Artur Georgynan (16-3) and Cuba’s Lorenzo Aragon (albeit by a tight 12-11 margin in the computer-scored bout) to reach the semis, where he faced reigning world amateur champion Serafim Todorov of Bulgaria.

What happened in that matchup likely remains Mayweather’s most indelibly bad memory in boxing, and to now is the last time he did not exit the ring a winner. No, the 10-9 decision that went against Mayweather isn’t as controversial as Jones’ “loss” to Si-Hun, but that’s only because it came in the semis instead of the title match. Mayweather left Atlanta with a consolation-prize bronze medal that wasn’t really much of a consolation at all.

For those who don’t remember the particulars, here’s what happened. Although Egyptian referee Hamadi Hafez Shouman did not deduct any penalty points from Todorov, although warning him numerous times for slapping, Shouman was so convinced that Mayweather must have won that he mistakenly raised the young American’s hand after the decision was announced.

U.S. boxing team leader Gerald Smith filed a protest with AIBA, complaining not only of the failure to penalize Todorov for alleged infractions, but because he believed that Olympic officials were hesitant to take action against anyone representing the home country of Emil Jetchen, a Bulgarian who served as AIBA’s chief of judges and referees.

“We feel the officials are intimidated where anyone competing against Mr. Jetchen’s fellow countrymen do not have a chance, as demonstrated in this bout,” Smith complained in his letter. Smith also claimed that Mayweather landed clean punches that did not count, and Todorov was awarded points on occasions when he threw punches that whiffed entirely or did not land to a scoring area.

Although the ’96 U.S. boxing team was generally successful when stacked against more recent editions, like the 2012 men’s squad that went to London and failed to bring back a single medal, the overall haul – a gold for 156-pounder David Reid and bronzes to Mayweather (125 pounds), Terrance Cauthen (132), Rhoshii Wells (165) and Antonio Tarver (178) – was less than expected, or maybe even deserved.

“Mayweather was the best defensive fighter on the team,” recalled Mitchell, whose longtime gig as the head boxing coach at the U.S. Olympic Education Center in Marquette, Mich., ended in early 2009, when the program was disbanded. “What surprised me is how he pressured the Cuban (Aragon) when they fought. I told him, `You can’t just rely on your defense or you’ll lose.’ And he did step it up on offense. He really surprised me.”

And the semifinal showdown against Todorov?

“Mayweather got the shaft,” Mitchell said. “He should have gone on to the final (in which Thailand’s Kamsing Somuck defeated Todorov, 8-5) and if he had, he would have won the gold medal. No question about that in my mind. I got all those Olympic fights on tape and I look at them quite a bit. I still can’t believe they screwed him like they did.”

The unexpected hero for the U.S. was Reid, who was trailing by 10 points entering the third and final round when he unleashed a thunderbolt of an overhand right that landed flush on the jaw of the heavily favored Cuban, Alfredo Duvergel, who went down and stayed down to the count of 10. The dramatic finish meant that Reid, not Mayweather or Tarver, got the big build-up and the big contract to turn pro. It was reported that Reid received a $1.5 million signing bonus and the guarantee of a $14.4 million over the life of a five-year deal to sign with a new promotional company, America Presents, although those figures were probably exaggerated.

“It is our belief that in five years David Reid will surpass $50 million in earnings,” the president of America Presents, Dan Goossen, said at the time. “This young man is a superstar waiting to happen.”

Reid went on to have a nice, albeit brief, pro career which was shortened by a persistent droopy left eyelid that several surgeries failed to correct. He retired with a 17-2 record, with seven wins inside the distance, and won the WBA super welterweight title in only his 12^th pro outing. After making two successful defenses, his championship was brutally claimed by Felix Trinidad, who overcame a third-round knockdown to floor the Philadelphian four times en route to a one-sided unanimous decision. Reid was never the same after that, going 3-1 against second-tier competition before retiring in 2001. For the past eight years Reid, who suffers from occasional bouts with depression and mood swings, has lived in a modest, two-bedroom apartment in Marquette, Mich. Almost all of his money from boxing is gone.

Contrast that with Mayweather, who signed with Top Rank, made a lot of money with that company and, after an acrimonious split with TR founder Bob Arum, makes even more now as the head of his own outfit, Mayweather Promotions. His nine previous PPV fights heading into the Guerrero bout have generated 9.6 million buys and $543 million in TV revenue, and he has appeared in the four biggest non-heavyweight PPV bouts in boxing history, No. 1 on the list being his May 5, 2005, split decision over Oscar De La Hoya, which did a whopping $136.85 million.

Life clearly is good for the Money Man, and apt to get even better if his insistence that defeat is not an option proves correct.

Still, I have to wonder if somewhere in the back of his mind is a nagging melancholia over his missed Olympic opportunity. More than a few millionaire pros have said their most lasting and satisfying memory in boxing came from representing their country on the brightly lit Olympic stage. Of course, those saying that more often than not came away with gold medals.

I would have asked Floyd about his reflections of his Olympic experience during last week’s teleconference, but a snafu with the automated process resulted in my not being placed in queue. Thus my inquiring mind did not learn if Mayweather’s psyche bears any scars from losing out on the gold he probably deserved, or if he has maintained any kind of relationship with his 1996 Olympic teammates, especially Reid.

So let’s leave it to Mitchell to fill in whatever blanks can be filled.

“I’m cool with Mayweather,” said Mitchell, whose fighters frequently work out in Mayweather’s Las Vegas gym when he and they are in town. “He treats me real good, and I think he’s gonna treat the fighters he has now (who are under contract to Mayweather Promotions) good. He takes care of them, tries to do right by them. That means so much when you’re a young fighter trying to get ahead.

“To tell the truth, he surprised me a little. Back in 1996, I thought he’d be really good, but maybe not this good. He always had lots of talent, but he’s shown he’s a smart businessman, too. He put himself in a position to succeed and he’s still succeeding.”

And is Mayweather’s relationship with other members of the ’96 U.S. Olympic boxing team as solid as with the young fighters he currently mentors?

“Until two years ago, he talked to (his former teammates) all the time,” Mitchell said. “Now … not so much. I don’t know why that is. That might be his choice. Maybe it isn’t. Time goes by and things change. Nobody said everything has to stay the same forever.

“You know, it’s kind of funny. At first, nobody on that ’96 team got along. There were about four different cliques. But in that last month before we left for Atlanta, everybody started to come together to work toward a common goal.

“Remember, that might have been America’s youngest team ever. We mostly had a bunch of kids, and they had to deal with that computer scoring. There wasn’t no boycotts either. All the big boxing countries were there.

“When people look back , they’re gonna say it was one of our better teams, no matter what the medal count was. Mayweather wasn’t the only one of our guys to get a bad decision. He just got the worst one. And you know what? They still did all right. What they did was unbelievable.”

The 1996 U.S. team produced five world champions in Mayweather, Reid, Tarver, Fernando Vargas and David Diaz. Three others – Eric Morel, Zahir Raheem and Rhoshii Wells – were challengers for widely recognized world titles. All in all, a good bit of collective success, if not exactly on a par with the renowned 1976 and ’84 squads.

Yet you wonder if Mayweather, the breakout star of that ’96 bunch, is headed for a fall if he continues to box past a point where the pendulum begins to swing back in the other direction. If Guerrero is not the pro equivalent of Serafim Todorov, isn’t it at least possible that Alvarez could be? Is there a judge or judges with faulty eyesight or a hidden bias who could contribute to the first smudge on Mayweather’s pro resume? And what if his remarkable skills eventually diminish to where he comes back to the pursuing pack?

Remember, then, Mitchell’s warning of what once was, and could be again. Nobody said everything has to stay the same forever.

It will be interesting to see how much of forever remains for the finest fighter of his era, beginning now.