Ali, 70, will receive the medal in a ceremony on Sept. 13 in Philadelphia at the National Constitution Center. The three-time world heavyweight champion was not in attendance for Thursday's announcement.

Previous recipients of the Liberty Medal, which was established in 1988 to celebrate the bicentennial of the U.S. Constitution, include rock singer and human rights activist Bono, former South African President Nelson Mandela and former President Jimmy Carter. Six winners have subsequently received the Nobel Peace Prize.

"Ali embodies the spirit of the Liberty Medal by embracing the ideals of the Constitution — freedom, self-governance, equality and empowerment — and helping to spread them across the globe," said former President Bill Clinton, chairman of the National Constitution Center, an institution dedicated to increasing public understanding of the Constitution and the ideas and values it represents.

Liberty Medal sponsors and partners said Ali's lifelong courage and conviction exemplify the qualities that the award was established to honor, from his outspoken advocacy for civil and religious freedom to his philanthropy, social activism and humanitarian efforts.

"Muhammad Ali symbolizes all that makes America great, while pushing us as a people and as a nation to be better," said National Constitution Center president and chief executive officer David Eisner. "Each big fight of his life has inspired a new chapter of civic action."

The fast-talking, boisterous fighter who referred to himself as "the greatest" was born Cassius Marcellus Clay Jr. on Jan. 17, 1942. He took up boxing at age 12 and flourished in the ring, becoming a top amateur and Olympic gold medalist.

Ali won the heavyweight title in 1964, defeating the heavily favored Sonny Liston. Soon after, Ali — who was raised in a Baptist family — announced his conversion to Islam and changed his name.

While in his prime, Ali was stripped of his heavyweight crown in 1967 for refusing to be inducted into the military during the Vietnam War because of his religious beliefs. The decision resulted in a draft-evasion conviction and spurred a long legal fight that ended in 1971, when the U.S. Supreme Court ruled in his favor.

Three years after his retirement from boxing in 1981, Ali announced he had Parkinson's disease, a degenerative brain condition that some researchers believe may be brought on by repeated blows to the head. Despite the diagnosis, he devoted himself to traveling the world on humanitarian missions bringing food and medical supplies to developing nations throughout the Middle East, Africa, South America and Asia. He also continues to work at home in the U.S. to raise funds for organizations including the Special Olympics and the Muhammad Ali Parkinson Research Center in Phoenix.

In 2005, Ali was awarded the Presidential Medal of Freedom. -- (AP)

While Keys talked about being pregnant and empathic when filming her documentary about AIDS in Africa, the U2 singer chimed in and said: "She's scary, isn't she? She's scary."

Bono went on to say that Keys has "lioness energy" and that her role as a new mother won't allow her to "let other mothers suffer."

He made the comments at the premiere of "Keep a Child Alive with Alicia Keys," a documentary which followed a visit to South Africa during last year's World Cup with a pregnant Keys and five Americans. It airs on Showtime on Dec. 1, which is World AIDS Day.

Bono said he met Keys when they recorded a cover of Marvin Gaye's "What's Going On" — with dozens of other musicians — in 2001.

"I was terrified the moment I met her. I was shaking in my boots," he said. "I was very moved by her singing of course, but what was interesting was the hard questions afterwards, and I think it's those hard questions that she asks that lead her."

Keys started her charity, Keep a Child Alive, in 2003. It assists those affected by HIV/AIDS in Africa and India.

She says she hopes the film reaches out to those who want to help, but can't make it to Africa.

"Even if you never have been able to travel there, or if you never can, that doesn't mean you can't travel with us and really see it for yourself," she said.

Bono says Keys has what it takes to make a difference in Africa, and around the world.

"Everyone's got heart, but actually you have to have the head for this," he said. "You have to be tough and strategic, you have to be demanding, (and) the money has to be spent well." If the money isn't spent well, he said, people get annoyed, "and so all these things take a certain intellectual rigor."

Keys has composed music for the Broadway play "Stick Fly," which debuts next week. When Bono — who along with the Edge wrote the music for "Spider-Man: Turn off the Dark" — was asked what advice he could give Keys, he said: "You know, it's an amazing American tradition, Broadway, and she can do anything she wants." -- (AP)