The legendary three-time world heavyweight champion passed away with his family by his side on Friday after being admitted to hospital earlier this week with a respiratory illness.

Ali had suffered from Parkinson's disease for more than 30 years, but his passing sent shockwaves far and wide despite such a long illness and his advancing years.

"I am the greatest, I said that even before I knew I was. I figured that if I said it enough, I would convince the world that I really was the greatest," was one of many famous lines from the inspirational American.

And high-profile figures from all over the planet did not need any convincing after the death of the late, great Ali.

United States of America President Barack Obama said: "Muhammad Ali shook up the world. And the world is better for it. We are all better for it. Michelle and I send our deepest condolences to his family, and we pray that the greatest fighter of them all finally rests in peace."

George Foreman said he will struggle "to think about a world without Muhammad Ali being alive", while Floyd Mayweather Jr, Serena Williams, Pele and Tiger Woods were among the sporting royalty to pay tributes.

Ali's daughter, Hana, revealed that her father's heart was beating for 30 minutes after his organs had failed as he fought right until the end.

She said "No one had ever seen anything like it. A true testament to the strength of his spirit and will!"

Family spokesman Bob Gunnell said Ali "did not suffer" and described his final moments with family as "solemn" but "beautiful".

"The champ would have been proud of his family," Gunnell said, adding it was "important to the family to have the celebration open to all walks of life" because Ali "was a citizen of the world".

When Ali make his last journey through Louisville on the way to the funeral on Friday he will travel on a boulevard named in his honour and mourners will be able to pay their respects at the Muhammad Ali Center.

A huge turnout is expected on the sidewalks and at the funeral, which will be open to the public, for an incredible character who will be remembered for taking a defiant stance against racism as well as his phenomenal exploits in the ring.