(CNN) -- Fifty-two years ago, a triumphant Muhammad Ali stood on top of a podium in Rome, representing the United States as a gold medalist in the heavyweight boxing division at the Summer Olympic games.
On Friday, the three-time heavyweight champion, whose name became synonymous with the phrases "float like a butterfly, sting like a bee" and "I am the Greatest," made another memorable appearance late Friday during a spectacular opening ceremony ushering in the 2012 Summer Olympic Games in London.
Appearing frail and in a white suit and tie, Ali was among a handful of dignitaries and other special guests who escorted the Olympic flag in the east London stadium. He then sat as the flag was raised, minutes before seven young promising athletes lit the Olympic cauldron.
Three decades ago, Ali was forced to retire from boxing following his diagnosis of Parkinson's disease although he never retreated from living a public life.
Ali arrived in London on Tuesday with his wife, Lonnie, in part, to raise money for the Muhammad Ali Center and promote Generation Ali, a social media site which focuses on educating young people about his core values, according to Ali Center spokeswoman Jeanie Kahnke. On Wednesday, Ali was honored at the Sports for Peace Gala and later met with U.S. Olympic athletes.
Ali's participation at the London games represented another poignant moment for him in opening ceremonies. In 1996, Ali brought millions of fans to tears at the Summer Olympic Games in Atlanta. With more than one billion worldwide viewers, the most recognized person in the world ascended the stadium steps with hands trembling but never wavering to light the lamp cauldron.
Outside the ring, Ali's influence as a humanitarian, mediator in world conflicts, civil rights crusader and fierce opponent of the Vietnam War, a stand which cost him his title and millions in earnings, all elevated his stature in modern history.
Ali was born Cassius Marcellus Clay Jr. in Louisville, Kentucky, in 1942 during an ugly era of racial segregation in America. At age 12, Ali's world changed forever when a white police officer introduced him to boxing. The sport became an outlet for his rage and offered the young man an opportunity to develop his remarkable talent.
Just months after he turned 18, Ali -- then still known as Clay -- won a gold medal at the 1960 Olympic Games in Rome. A hometown parade in his honor would soon be overshadowed by racism when Clay was refused service in a white-owned restaurant because of Jim Crow laws and racial bigotry. In his memoir, "The Greatest," he wrote that he tossed the medal into a Louisville river in disgust over racial prejudice in America.
Four years after his pro debut, Clay's biggest moment had arrived, a title shot at the heavyweight championship against a fighter most experts thought was invincible, Sonny Liston. Despite 7 to 1 odds, the young Clay began a relentless assault of verbal attacks calling Liston "the big ugly bear."
Clay's verbal taunts shifted into a flurry of fast and precise jabs, unleashing a volley of punches from every angle. By the end of the fight, Liston's face was bleeding, and his was physically and mentally broken. The fight was over, and the boxing world was stunned.
"I shook up the world, I shook up the world," proclaimed Ali as he pushed his way through a swarm of journalists and supporters in the ring.
To prove the point that a new champion had ascended, Clay put Liston away for a second time in a rematch the following year.
The 1960s were glory days for the young champion, but the civil rights era became a controversial and polarizing period in his life. He renounced his given name of Cassius Clay and joined the black separatist Nation of Islam. "Ali was a child of the South and understood racial segregation, he watched as black people were beaten, bitten by dogs and lynched and all of that had an impact on him," said sports sociologist and University of California professor emeritus Harry Edwards.
When he wasn't in the ring, Ali often found himself at the center of civil rights protests and rising black anger over white resistance to racial integration.
"Self determination was a powerful image at that time and instead of striving to share space with people who hated blacks, Ali took the position that "we as black men are able to stand on our own feet, develop our own institutions and be men," Edwards said.
In spite of Ali's alliance with the Nation of Islam and its philosophy of black separation, Ali's lifelong trainer, Angelo Dundee, the son of a white rail road worker, remained a close confidant. In his memoir, "My View from the Corner: A Life in Boxing," Dundee said of Ali, "I never heard anything resembling a racist comment leave his mouth. There was never a black-white divide." In a sport where fighter-trainer relationships rarely last, Dundee and Ali would never separate.
Ali's World Boxing Association heavyweight title was revoked after he claimed conscientious objector status and refused to serve in the Vietnam War. "I ain't got no quarrel with them Vietcong," Ali said after his draft. At the peak boxing age of 25, Ali gave up tens of millions of dollars in endorsements and faced five years in prison in defiance of a war that he called "despicable and unjust." To earn a living, Ali made television appearances and spoke on college campuses, joining anti-war protesters.
Ali would fight his case all the way to the U.S. Supreme Court, where his conviction was later overturned on a technicality.
"When Ali put everything he achieved on the line in difference to his religion and political principles that got attention around the world," said Edwards. "People eventually came to believe Ali was sincere and over time there developed a tremendous degree of unquestioned integrity about him."
By 1970, the anti-war sentiment had gathered momentum, and the next decade would mark a turning point in Ali's life. In 1971, Ali was back, and the stage was set for a showdown between the undefeated Ali and unbeaten WBA champion Joe Frazier. Each man was guaranteed $2.5 million, the biggest boxing payday ever in the sport for a bout seen by an estimated 300 million viewers worldwide.
Their rivalry would become epic and intensely personal with constant verbal taunting from Ali. On March 8, 1971, at Madison Square Garden the match dubbed "The Fight of the Century" began with both fighters engaged a series of powerful punches and counter attacks. In the 15th round, Frazier unleashed a devastating left hook that caught Ali on the jaw, knocking him to the ground. It would be only the third time Ali had been knocked down in his career and led to his first professional defeat.
He won a 1974 rematch with Frazier, earning another shot at the heavyweight champion title, which would turn out to be the fight of his career and one of the most memorable events in sports history.
"The Rumble in the Jungle" in central Africa put Ali against fearsome champion George Foreman, a 3-to-1 favorite. In what is considered to be his best tactical fight, Ali once again stunned the boxing world declaring, "I told you all that I was the greatest of all time."
By reclaiming the heavyweight title, Ali and Frazier were poised to meet again for a third and final time. On October 1, 1975, the "Thrilla in Manila," as it became, known took place at the Philippine Coliseum outside the capital, Manila. While Frazier voiced no political views and could not match Ali's charisma, he was characterized as the favorite of the establishment.
Ali's assault would take its final toll, when Frazier, deeply battered, with one eye swollen and shut, was unable to come out and face Ali for the 15th round.
When the fight was stopped, Ali remained ahead on the scorecards of all three judges. In a post-fight news conference Ali said, "It's the closest I've come to death."
Ali's third comeback and victory over Leon Spinks in 1978 allowed him to claim the heavyweight title for a record third time.
His last professional fight in 1981 marked the beginning of another battle that Ali described as his toughest, the diagnosis three years later that he was afflicted with Parkinson's disease. After two decades of redefining the heavyweight division, Ali was forced to retire with a lifetime record of 56 victories and five defeats.
Although his physical condition deteriorated, Ali continued to assert his influence in the humanitarian community. He served as a mediator in world conflicts, primarily throughout the Middle East, Asia and Africa. In 1990, before the first Gulf war, Ali personally visited former Iraqi leader Saddam Hussein and secured the release of 14 U.S. citizens held captive and used as human shields.
"The fact that he was a serious and dedicated Muslim devoted to put everything on the line, including his life, in a culture like Iraq. Iif Ali comes in and says, 'Let these people go,' even a monster such as Hussein could probably at some level be moved by his humanity," said Edwards, the historian.
Serving as a U.N. Messenger of Peace, Ali has visited over 100 countries, meeting world leaders, monarchs and human rights agencies to provide humanitarian assistance.
Ali was voted the greatest athlete of the 20th century by Sports Illustrated, where he'd appeared as a cover story more times than any other athlete. Upon his selection, his wife, Lonnie, told CNN, "There is no more fitting symbol for the civil rights era than this man who defied all the rules, refusing to be silenced and did it all with style and grace because of his unrelenting pursuit of peace and racial equality."
In 2005, Ali was presented with the nation's highest civilian honor, the presidential Medal of Freedom.
"My father's spirit has experienced and survived many challenges," said his daughter Hana Ali, who co-authored his autobiography, "The Soul of a Butterfly: Reflections on Life's Journey."
According to Hana Ali, the heavyweight champion was never content with simply winning titles. "I've always wanted to be more than just a boxer," she quoted him as saying.
"I wanted to use my fame and this face that everyone knows so well to help uplift and inspire people around the world. I've made my share of mistakes along the way, but if I have changed even one life for the better, I haven't lived in vain," her father said, according to Hana Ali.
While Parkinson's disease may have robbed Ali of the physical traits he treasured the most -- his fluid, eloquent moves -- his commitment to humanity has never wavered.
Downtown Louisville, a city that once forbid Ali from sharing the same public facilities with whites, now includes the Muhammad Ali Center. The center promotes Ali's six core values: respect, confidence, conviction, dedication, spirituality and giving. Inside the cultural center and museum, Ali's voice can be heard on plasma screens, reminding those who tried to silence him that "The Greatest" has lived up its name.
"Ali's got a left, Ali's got a right, when he knocks you down, you'll sleep for the night and when you lie on the floor and the ref counts to ten, hope and pray that you never meet me again," says Ali.