See Boxing Legend Muhammad Ali’s Tribute to Nelson Mandela

Muhammad Ali paid tribute to Nelson Mandela as a symbol of forgiveness who inspired others to "reach for what appeared to be impossible," as the boxing great joined in mourning the death of the South African anti-apartheid leader Thursday.

The icons who shared a boxing background met twice — once in South Africa and once in North America, said a spokeswoman for the Ali Center in Louisville, Ali's hometown.

"What I will remember most about Mr. Mandela is that he was a man whose heart, soul and spirit could not be contained or restrained by racial and economic injustices, metal bars or the burden of hate and revenge," Ali said in his statement released by the Ali Center. "He taught us forgiveness on a grand scale."

Mandela emerged from 27 years in prison to negotiate an end to white minority rule in South Africa. He later became the country's first black president.

"He inspired others to reach for what appeared to be impossible and moved them to break through the barriers that held them hostage mentally, physically, socially and economically," Ali said. "He made us realize, we are our brother's keeper and that our brothers come in all colors."

Among the exhibits at the Ali Center is a photo of Ali and Mandela, their hands clenched into fists as if they're boxing.

That photo was taken during Ali's trip to South Africa, said Ronald DiNicola, Ali's longtime attorney who accompanied the boxing great on the trip.