Muhammad Ali, a three-time heavyweight boxing champion who transcended sports with his outspoken stances on religious, political, and social issues, died on Friday at a Phoenix-area hospital where he was receiving treatment for respiratory problems. He was 74.

Ali was famed for verbal dexterity as much for his prowess in the ring, a legacy summed up by his mantra "float like a butterfly, sting like a bee." He became one of the most important public figures during the 1960s and '70s after speaking out about civil rights issues and the US war in Vietnam.

In 1964, two days after he knocked out Sonny Liston to become heavyweight champ for the first time at age 22, the Louisville, Kentucky native joined the Nation of Islam, a religion made famous by civil rights leader Malcolm X. After changing his name from Cassius Clay, Ali continued to dominate the boxing world and became a lightning rod for political dissent during a tumultuous era in America.

On April 28, 1967, at the height of the Vietnam War, Ali refused to be drafted into the US Army, citing his religious beliefs. "I ain't got no quarrel with them Vietcong," he famously said. He was later convicted of refusing induction into the US Armed Forces and sentenced to five years in prison. The Supreme Court eventually ruled in his favor, but Ali was stripped of his title and barred from boxing for nearly four years. The controversy, combined with his extremely colorful character, made Ali more than an athlete.

"Once, we viewed sports as a world apart, untouched by the political and economic and racial problems of the day," wrote Randy Roberts in a recent book about Ali. "Well, since Muhammad Ali, we can never maintain that fiction."

Later in life, Ali's ability to turn a phrase was diminished by his battle with Parkinson's Disease — an affliction his family blamed on his years of fighting — but that did not deter him from weighing in on more recent debates.

The hometown newspaper remembers a hometown hero as the world mourns Muhammad Ali — Mayor Greg Fischer (@louisvillemayor)June 4, 2016

Last December, after the mass shooting in San Bernardino, California that killed 14 people and injured 22 others, presumptive Republican presidential nominee Donald Trump called for a "total and complete shutdown of Muslims entering the United States," citing the fact that the two shooters in the incident were radical Muslims who authorities said were inspired by the Islamic State.

Ali, who left the Nation of Islam in 1975 and converted to the more mainstream Sunni denomination, took the opportunity to defend Islam as a religion of peace.

"I am a Muslim and there is nothing Islamic about killing innocent people in Paris, San Bernardino, or anywhere else in the world, "Ali wrote. "True Muslims know that the ruthless violence of so called Islamic jihadists goes against the very tenets of our religion."

Ali called on Muslims to "stand up to those who use Islam to advance their own personal agenda."

He added that the radical jihadists responsible for the terror attacks in Paris and San Bernardino "have alienated many from learning about Islam. True Muslims know or should know that it goes against our religion to try and force Islam on anybody."

On Saturday, Trump tried to join the chorus of mourners paying their respects to Ali on social media, tweeting that the boxer was "a truly great champion and a wonderful guy."

Muhammad Ali is dead at 74! A truly great champion and a wonderful guy. He will be missed by all! — Donald J. Trump (@realDonaldTrump)June 4, 2016

But many were quick to call Trump out, reminding him of his remarks on Twitter in December when he criticized President Barack Obama for delivering a speech that mentioned Muslim sports heroes. "What sport is he talking about, and who?" Trump asked. "Is Obama profiling?"

Obama said in his speech that Muslims are our sports heroes. What sport is he talking about, and who? Is Obama profiling? — Donald J. Trump (@realDonaldTrump)December 7, 2015

Without naming Trump, Ali's remarks after the San Bernardino shooting criticized the presidential candidate for his proposed Muslim ban.

"Speaking as someone who has never been accused of political correctness, I believe that our political leaders should use their position to bring understanding about the religion of Islam and clarify that these misguided murderers have perverted people's views on what Islam really is," Ali said.

On Saturday, Obama released a heartfelt statement describing why Ali mattered. The president described keeping a pair of Ali's boxing gloves on display in his private study just off the Oval Office, along with the iconic photograph of Ali "roaring like a lion over a fallen Sonny Liston."

"I was too young when it was taken to understand who he was — still Cassius Clay, already an Olympic Gold Medal winner, yet to set out on a spiritual journey that would lead him to his Muslim faith, exile him at the peak of his power, and set the stage for his return to greatness with a name as familiar to the downtrodden in the slums of Southeast Asia and the villages of Africa as it was to cheering crowds in Madison Square Garden," Obama wrote, referencing legendary title fights by Ali in the Philippines and Zaire, which is now the Democratic Republic of Congo.

He shook up the world, and the world's better for it. Rest in peace, Champ. — President Obama (@POTUS)June 4, 2016

""I am America,'" Obama wrote, quoting Ali, "'I am the part you won't recognize. But get used to me – black, confident, cocky; my name, not yours; my religion, not yours; my goals, my own. Get used to me.'"

Obama noted that Ali supported the struggles of Martin Luther King Jr. and Nelson Mandela, and that he "spoke out when others wouldn't."

"Muhammad Ali was The Greatest," Obama said. "Period."

One of the most beautiful tributes to Muhammad Ali you will read today or any day: from — Samantha Power (@AmbassadorPower)June 4, 2016

Aside from Obama, many other notable figures also remembered Ali on Saturday, including Sadiq Khan, London's first Muslim mayor.

Muhammad Ali was not just a boxing legend, but a civil rights champion and a towering figure of our time — Mayor of London (@MayorofLondon)June 4, 2016

Muhammad Ali was my hero - a phenomenal champion who broke down barriers throughout the world. — Sadiq Khan (@SadiqKhan)June 4, 2016

Fellow boxing greats Mike Tyson and George Foreman, who was Ali's foe in the legendary "Rumble in the Jungle" match in 1974, also took to Twitter to remember Ali.

Until Ali no one said 'I'm beautiful' he was royalty, yet common man was his pal. That is beauty. Greatest kind — George Foreman (@GeorgeForeman)June 4, 2016

But perhaps the most fitting tribute came from author JK Rowling, who posted a quote from Ali that described how "The Greatest" hoped to be remembered after his death.