“You could spend 20 years studying Ali,” Dave Kindred once wrote, “and still not know what he is or who he is.

“He’s a wise man, and he’s a child. I’ve never seen anyone who was so giving and, at the same time, so self-centered. He’s either the most complex guy that I’ve ever been around or the most simple. And I still can’t figure out which it is. I mean, I truly don’t know. We were sure who Ali was only when he danced before us in the dazzle of the ring lights. Then he could hide nothing.”

And so it was that the world first came to know Muhammad Ali not as a person — not as a social, political or religious figure — but as a fighter. His early professional bouts infuriated and entertained as much as they impressed. Cassius Clay held his hands too low. He backed away from punches, rather than bobbing and weaving out of danger, and he lacked true knockout power. Purists cringed when he predicted the round in which he intended to knock out his opponent, and grimaced when he did so and bragged about each new conquest.

Then, at age 22, Clay challenged Sonny Liston for the world heavyweight crown.

Liston was widely regarded as the most intimidating, ferocious, powerful fighter of his era. Clay was such a prohibitive underdog that Robert Lipsyte, who covered the bout for The New York Times, was instructed to “find out the directions from the arena to the nearest hospital, so I wouldn’t waste deadline time getting there after Clay was knocked out.”

But as David Ben-Gurion once proclaimed, “Anyone who doesn’t believe in miracles is not a realist.” Cassius Clay knocked out Sonny Liston to become heavyweight champion of the world.

Officially, Ali’s reign as champion was divided into three segments. And although he fought through the administrations of seven presidents, his greatness as a fighter was most clearly on display during the three years after he first won the crown. During the course of 37 months, Ali fought 10 times. No heavyweight in history has defended his title more frequently against more formidable opposition in more dominant fashion than Ali did in those years.

Boxing, in the first instance, is about not getting hit. “And I can’t be hit,” Ali told the world.

“It’s impossible for me to lose because there’s not a man on earth with the speed and ability to beat me.”

In his rematch with Liston, which ended in a first-round knockout, Ali was hit only twice.

Victories over Floyd Patterson, George Chuvalo, Henry Cooper, Brian London and Karl Mildenberger followed.

Then, on Nov. 14, 1966, Ali waged battle with Cleveland Williams.

Over the course of three rounds, Ali landed more than 100 punches, scored four knockdowns and was hit a total of three times.

“The hypocrites and phonies are all shook up because everything I said would come true, did come true,” Ali chortled afterward. “I said I was the greatest, and they thought I was just acting the fool. Now, instead of admitting that I’m the best heavyweight in all history, they don’t know what to do.”

Ali’s triumph over Williams was followed by victories over Ernie Terrell and Zora Folley. Then, after refusing induction into the United States Army, Ali was stripped of his title and forced out of boxing.

“If I never fight again, this is the last of the champions,” Ali said of his, and boxing’s, plight. “The next title is a political belt, a racial belt, an organization belt. There’s no more real world champion until I’m physically beat.”

In October 1970, Ali was allowed to return to boxing, but his skills were no longer the same.

The legs that had allowed him to “dance” for 15 rounds without stopping no longer carried him as surely around the ring. His reflexes, while still superb, were no longer lightning-fast. Ali prevailed in his first two comeback fights, against Jerry Quarry and Oscar Bonavena. Then he challenged Joe Frazier, who was the “organization” champion by virtue of victories over Buster Mathis and Jimmy Ellis.

“Champion of the world? Ain’t but one champion,” Ali said before his first bout against Frazier.

“How you gonna have two champions of the world? He’s an alternate champion. The real champion is back now.”

But Frazier thought otherwise.

And on March 8, 1971, he bested Ali in 15 brutal rounds.

“He’s not a great boxer,” Ali said afterward.

“But he’s a great slugger, a great street fighter, a bull fighter. He takes a lot of punches, his eyes close, and he just keeps coming. I figured he could take the punches. But one thing surprised me in this fight, and that’s that he landed his left hook as regular as he did. Usually, I don’t get hit over and over with the same punch, and he hit me solid a lot of times.”

Some fighters can’t handle defeat. They fly so high when they’re on top that a loss brings them irrevocably crashing down.

Said Ferdie Pacheco, Ali’s cornerman and physician: “What was interesting to me after the loss to Frazier was, we’d seen this undefeatable guy; now, how was he going to handle defeat? Was he going to be a crybaby? Was he going to be crushed? Well, what we found out was, this guy takes defeat like he takes victory. All he said was, ‘I’ll beat him next time.'”

What Ali said was plain and simple: “I got to whup Joe Frazier because he beat me. Anybody would like to say, ‘I retired undefeated.’ I can’t say that no more. But if I could say, ‘I got beat, but I came back and beat him,’ I’d feel better.”

Following his loss to Frazier, Ali won 10 fights in a row — eight of them against world-class opponents.

Then, in March 1973, he stumbled when a little-known fighter named Ken Norton broke his jaw in the second round en route to a 12-round upset decision.

“I knew something was strange,” Ali said after the bout, “because if a bone is broken, the whole internalness in your body, everything, is nauseating. I didn’t know what it was, but I could feel my teeth moving around, and I had to hold my teeth extra tight to keep the bottom from moving.

“My trainers wanted me to stop. But I was thinking about those 19,000 people in the arena, and [ABC’s] ‘Wide World of Sports,’ millions of people at home watching in 62 countries. So what I had to do was put up a good fight, go the distance and not get hit on the jaw again.”

Now Ali had a new target — a priority ahead of even Frazier.

“After Ali got his jaw broke, he wanted Norton bad,” recalled Lloyd Wells, a longtime Ali confidante.

“[Ali’s manager] Herbert Muhammad was trying to put him in another fight, and Ali kept saying, ‘No, get me Norton. I want Norton.’ Herbert was saying, ‘But we got a big purse,’ we got this and we got that. And Ali was saying, ‘No, just get me Norton. I don’t want nobody but Norton.'”

Ali got Norton — and beat him.

Then, after an interim bout against Rudi Lubbers, he got Frazier again — and beat him, too.

From a technical point of view, the second Ali-Frazier bout was probably Ali’s best performance after his exile from boxing. He did what he wanted to do, showing flashes of what he once had been as a fighter, but never would be again. Then Ali journeyed to Zaire to challenge George Foreman, who had dethroned Frazier to become heavyweight champion of the world.

“Foreman can punch but he can’t fight,” Ali said of his next foe.

But most observers thought Foreman could do both. As was the case when Ali fought Sonny Liston, he entered the ring a heavy underdog.

Still, studying his opponent’s armor, Ali thought he detected a flaw: Foreman’s punching power was awesome, but his stamina and will were suspect. Thus, the “rope-a-dope” was born.

“The strategy on Ali’s part was to cover up because George was like a tornado,” said former light heavyweight great Archie Moore, who was one of Foreman’s cornermen that night. “And when you see a tornado coming, you run into the house and you cover up. You go into the basement and get out of the way of that strong wind because you know that otherwise it’s going to blow you away. That’s what Ali did. He covered up and the storm was raging. But after a while, the storm blew itself out.”

Or as phrased by prominent sportswriter Jerry Izenberg: “Yeah, Ali let Foreman punch himself out.

“But the rope-a-dope wouldn’t have worked against Foreman for anyone in the world except Ali because, on top of everything else, Ali was tougher than everyone else. No one in the world except Ali could have taken George Foreman’s punches.”

Ali stopped Foreman in the eighth round to regain the heavyweight championship.

Over the next 30 months, at the peak of his popularity as champion, Ali fought nine times. Those bouts showed him to be a courageous fighter, but a fighter on the decline.

Like most aging combatants, he did his best to put a positive spin on things. But viewed in realistic terms, “I’m more experienced” translated into “I’m getting older.” “I’m stronger at this weight” meant “I should lose a few pounds.” “I’m more patient now” was a cover for “I’m slower.”

Eight of Ali’s first nine fights during his second reign as champion did little to enhance his legacy. But sandwiched in between matches against the likes of Jean-Pierre Coopman and Richard Dunn and mediocre showings against more legitimate adversaries, Ali won what might have been the greatest fight of all time.

On Oct. 1, 1975, Ali and Frazier met in the Philippines, six miles outside of Manila, to do battle for the third time.

“You have to understand the premise behind that fight,” Pacheco said afterward. “The first fight was life and death, and Frazier won. Second fight: Ali figures him out, no problem; relatively easy victory for Ali. Then Ali beats Foreman, and Frazier’s sun sets. And I don’t care what anyone says now, all of us thought that Joe Frazier was shot. We all thought that this was going to be an easy fight. Ali comes out, dances around and knocks him out in eight or nine rounds. That’s what we figured.

“And you know what happened in that fight. Ali took a beating like you’d never believe anyone could take. When he said afterward that it was the closest thing he’d ever known to death — let me tell you something: If dying is that hard, I’d hate to see it coming. But Frazier took the same beating. And in the 14th round, Ali just about took his head off. I was cringing.

“The heat was awesome; both men were dehydrated. The place was like a time bomb. I thought we were close to a fatality. It was a terrible moment, and then Joe Frazier’s corner stopped it.”

“Ali-Frazier III was Ali-Frazier III,” Izenberg said. “There’s nothing to compare it with. I’ve never witnessed anything like it. And I’ll tell you something else: Both fighters won that night, and both fighters lost.”

“The human brain wasn’t meant to get hit by a heavyweight punch,” Pacheco later noted. “And the older you get, the more susceptible you are to damage. When are you best? Between 15 and 30. At that age, you’re growing, you’re strong, you’re developing. You can take punches and come back. But inevitably, if you keep fighting, you reach an age when every punch can cause damage. Nature begins giving you little bills, and the amount keeps escalating — like when you owe money to the IRS and the government keeps adding and compounding the damage.”

In Manila, Frazier landed 440 punches; many of them to Ali’s head. After Manila would have been a good time for Ali to stop boxing, but too many people had a vested interest in his continuing to fight. Harold Conrad served for years as a publicist for Ali’s bouts. “You get a valuable piece of property like Ali,” Conrad said shortly before his own death, “how are you going to put it out of business? It’s like shutting down a factory or closing down a big, successful corporation. The people who are making money off the workers just don’t want to do it.”

Thus, Ali fought on. In 1977, he was hurt badly but came back to win a close decision over Earnie Shavers. “In the second round, I had him in trouble,” Shavers remembered. “I threw a right hand over Ali’s jab, and I hurt him. He kind of wobbled. But Ali was so cunning, I didn’t know if he was hurt or playing fox. I found out later that he was hurt; but he waved me in, so I took my time to be careful. I didn’t want to go for the kill and get killed. And Ali was the kind of guy who, when you thought you had him hurt, he always seemed to come back. The guy seemed to pull off a miracle each time. I hit him with a couple of good shots, but he recovered better than any other fighter I’ve known.”

Next up for Ali was Leon Spinks, a novice with an Olympic gold medal but only seven professional fights.

“Spinks was in awe of Ali,” recalled Ron Borges of the Boston Globe. “The day before their first fight, I was having lunch in the coffee shop at Caesar’s Palace with Leon and [his trainer] Sam Solomon. No one knew who Leon was. Then Ali walked in, and everyone went crazy. ‘Look, there’s Ali! Oh my god, it’s him!’ And Leon was like everybody else. He got all excited. He was shouting, ‘Look, there he is! There’s Ali!’ In 24 hours, they’d be fighting each other, but right then, Leon was ready to carry Ali around the room on his shoulders.”

The next night, Spinks captured Ali’s title with a relentless 15-round assault. Seven months later, Ali returned the favor, regaining the championship with a 15-round victory of his own. He then retired from boxing, but two years later made an ill-advised comeback against Larry Holmes.

“Before the Holmes fight, you could clearly see the beginnings of Ali’s physical deterioration,” said Barry Frank, who at the time was representing Ali in various commercial endeavors on behalf of IMG. “The huskiness had already come into his voice, and he had a little bit of a balance problem. Sometimes he’d get up off a chair and, not stagger, but maybe take a half-step to get his balance.”

Realistically speaking, it was obvious that Ali had no chance of beating Larry Holmes. But there was always that kernel of doubt. Would beating Holmes be any more extraordinary than knocking out Sonny Liston and George Foreman? Ali himself fanned the flames.

“I’m so happy going into this fight,” he said shortly before the bout. “I’m dedicating this fight to all the people who’ve been told, ‘You can’t do it.’ People who drop out of school because they’re told they’re dumb. People who go do crime because they don’t think they can find jobs. I’m dedicating this fight to all of you people who have a Larry Holmes in your life. I’m gonna whup my Holmes, and I want you to whup your Holmes.”

But Holmes put it more succinctly: “Ali is 38 years old. His mind is making a date that his body can’t keep.”

Holmes was right. It was a horrible night. Old and seriously debilitated from the effects of an improperly prescribed drug called Thyrolar, Ali was a shell of his former self. He had no reflexes, no legs, no punch. Nothing, except his pride and the crowd chanting, “Ali! Ali!”

“I really thought something bad might happen that night,” Izenberg later recalled. “And I was praying that it wouldn’t be the something that we dread most in boxing. I’ve been at three fights where fighters died, and it sort of found a home in the back of my mind. I was saying, ‘I don’t want this man to get hurt.’ Whoever won the fight was irrelevant to me.”

It wasn’t an athletic contest, just a brutal beating that went on and on. Later, some observers claimed that Holmes lay back because of his fondness for Ali. But Holmes was being cautious, not compassionate. “I love the man,” he said afterward. “But when the bell rung, I didn’t even know his name.”

“By the ninth round, Ali had stopped fighting altogether,” said Lloyd Wells, Ali’s advisor. “He was just defending himself, and not doing a good job of that. Then, in the ninth round, Holmes hit him with a punch to the body, and Ali screamed. I never will forget that as long as I live: Ali screamed.”

The fight was stopped after 11 rounds. An era in boxing — and an entire historical era — was over. And now, years later, in addition to his more important social significance, Ali is recognized by some as the greatest fighter of all time. He was graced with almost unearthly physical skills and did everything his body allowed him to do. In a sport that is often brutal and violent, he cast a long and graceful shadow.

How good was Ali?

“In the early days,” Pacheco said, “he fought as though he had a glass jaw and was afraid to get hit. He had the hyper reflexes of a frightened man. He was so fast that you had the feeling, this guy is scared to death; he can’t be that fast normally. Well, he wasn’t scared. He was fast beyond belief, and smart.

“Then he went into exile; and when he came back, he couldn’t move like lightning anymore. Everyone wondered, ‘What happens now when he gets hit?’ That’s when we learned something else about him: That sissy-looking, soft-looking, beautiful-looking, child-man was one of the toughest guys who ever lived.”

Ali didn’t have one-punch knockout power. His most potent offensive weapon was speed, the speed of his jab and straight right hand. But when he sat down on his punches, as he did against Joe Frazier in Manila, he hit harder than most heavyweights. And in addition to his other assets, he had superb footwork, the ability to take a punch and all of the intangibles that go into making a great fighter.

“Ali fought all wrong,” Izenberg said. “Boxing people would say to me, ‘Any guy who can do this will beat him. Any guy who can do that will beat him.’ And after a while, I started saying back to them, ‘So you’re telling me that any guy who can outjab the fastest jabber in the world can beat him. Any guy who can slip that jab — which is like lightning — not get hit with a hook off the jab, get inside and pound on his ribs can beat him. Any guy. Well, you’re asking for the greatest fighter who ever lived, so this kid must be pretty good.'”

And on top of everything else, the world never saw Muhammad Ali at his peak as a fighter. When Ali was forced into exile in 1967, he was getting better with virtually every fight. The Ali who fought Cleveland Williams, Ernie Terrell and Zora Folley was bigger, stronger, more confident and more skilled than the 22-year-old who, three years earlier, had defeated Sonny Liston. But when Ali returned, his ring skills were diminished. He was markedly slower and his legs weren’t the same.

“I was better when I was young,” Ali acknowledged later. “I was more experienced when I was older. I was stronger; I had more belief in myself. Except for Sonny Liston, the men I fought when I was young weren’t near the fighters that Joe Frazier and George Foreman were. But I had my speed when I was young. I was faster on my legs, and my hands were faster.”

Thus, the world never saw what might have been. What it did see, though, in the second half of Ali’s career, was an incredibly courageous fighter. Not only did Ali fight his heart out in the ring, he fought the most dangerous foes imaginable. Many champions avoid facing tough challengers. When Joe Louis was champion, he refused to fight certain black contenders. After Joe Frazier defeated Ali, his next defenses were against Terry Daniels and Ron Stander. Once George Foreman won the title, his next bout was against Jose Roman.

But Ali had a different creed: “I fought the best,” he said, “because if you want to be a true champion, you got to show people that you can whup everybody.”

“I don’t think there’s a fighter in his right mind that wouldn’t admire Ali,” Earnie Shavers said. “We all dreamed about being just half the fighter that Ali was.”

And of course, each time Ali entered the ring, the pressure on him was palpable. “It’s not like making a movie where, if you mess up, you stop and reshoot,” Ali said shortly before Ali-Frazier III. “When that bell rings and you’re out there, the whole world is watching and it’s real.”

But Ali was more than a great fighter. He was the standard-bearer for boxing’s modern era. The 1960s introduced athletes who were bigger and faster than their predecessors, and Ali was the prototype for that mold. He was also part and parcel of the changing economics of boxing. Ali arrived just in time for the advent of satellites and closed-circuit television. He carried heavyweight championship boxing beyond the confines of the United States and popularized the sport around the globe.

Almost always, the public sees boxers as warriors without ever realizing their soft human side. But the whole world saw Ali’s humanity. “I was never a boxing fan until Ali came along” is a frequent refrain. And although “the validity of boxing is always hanging by a thread,” said England’s Hugh McIlvanney (who coined that phrase), “Ali was boxing’s salvation.”

An Ali fight was always an event. Ali put that in perspective when he said, “I truly believe I’m fighting for the betterment of people. I’m not fighting for diamonds or Rolls-Royces or mansions, but to help mankind. Before a fight, I get myself psyched up. It gives me more power, knowing there’s so much involved and so many people are gonna be helped by my victory.”

To which journalist and TV host Gil Noble added: “When Ali got in the ring, there was a lot more at stake than the title. When that man got in the ring, he took all of us with him.”

For virtually his entire career, being around Ali was fun. Commenting on young Cassius Clay, Don Elbaum remembered: “I was the matchmaker for a show in Pittsburgh when he fought Charlie Powell. We were staying at a place called Carlton House. And two or three days before the fight, Cassius, which was his name then, decided to visit a black area of Pittsburgh. It was winter, real cold. But he went out, walking the streets, just talking to people. And I’ve never seen anything like it in my life. When he came back to the hotel around 6 o’clock, there were three hundred people following him. The Pied Piper couldn’t have done any better. And the night of the fight, the weather was awful. There was a blizzard; the schools were shut down. Snow kept falling; it was windy. Conditions were absolutely horrible. And the fight sold out.”

Some athletes are engaging when they’re young and lose their charm as their celebrity status grows. But Michael Katz, then with the New York Times, recalled the day when Ali, at the peak of his popularity, defended his title against Richard Dunn: “On the day of the fight, Ali got bored, so he decided to hold a press conference. Word got around; Ali came downstairs and we went to a conference room in the hotel, but it wasn’t set up yet. So every member of the press followed him around. We were like mice, going from room to room until finally the hotel management set us up some place. And Ali proceeded to have us all in stitches. He imitated every opponent he’d ever fought, including Richard Dunn, who he hadn’t fought yet. And he was marvelous. You’d have paid more money to see Muhammad Ali on stage at that point than you’d pay today for [a top entertainer].”

And Ali retained his charm when he got old.

“The first Ali fight I ever covered,” Borges said, “was the one against Leon Spinks, where Ali had said it made him look silly to talk up an opponent with only seven professional fights, so he wasn’t talking. And I said to myself, ‘Great. Here I am, a young reporter about to cover the most verbally gifted athlete in history, and the man’s not talking.’

“Anyway, I was at one of Ali’s workouts. Ali finished sparring, picked up a microphone and told us all what he’d said before: ‘I’m not talking.’ Then he went on for about 90 minutes. Typical Ali — the funniest monologue I’ve ever heard. And when he was done, he put the microphone down, smiled that incredible smile and told us all, ‘But I’m not talking.’

“I’ll always remember the joy of being around Ali,” Borges said. “It was fun. And covering the heavyweights isn’t much fun anymore. Ali took that with him when he left, and things have been pretty ugly lately.”

Muhammad Ali did too much for boxing. And the sport isn’t the same without him.

Thomas Hauser is the author of 32 books, including the definitive Ali biography, “Muhammad Ali: His Life and Times.” Hauser can be reached by email at thauser@rcn.com.