Boxing is a brutal sport and Muhammad Ali appears to have paid the price. The “float like a butterfly, sting like a bee” arrogant young boxer became a shuffling, slurring, gentle giant in his last years.
Like many people with rich personalities, who he was in his private life is a bit of a mystery. But no one can deny that he had personality. His quips are priceless:

"It's just a job. Grass grows, birds fly, waves pound the sand. I beat people up."
“If they can make penicillin out of moldy bread, they can sure make something out of you.”
"I should be a postage stamp. That's the only way I'll ever get licked."
“If you even dream of beating me you'd better wake up and apologize.”

But he was more than the Louisville Lip, more than a philandering ex-boxer who had four wives and fathered nine children. He seemed to grow as a man with time and suffering.
One aspect of that was his religious faith. After defeating Sonny Liston in 1964 for the world heavyweight title, he announced that he had become a Muslim, or rather, a member of the Nation of Islam, an American sect of Islam. Later he drifted into mainstream Sunni Islam and then into the more mystical, peaceful Sufi version of Islam.
In this video he gives an amazingly frank explanation of what he believes about the importance of the afterlife.
Vale, Muhammad Ali. As he once said,

“Live everyday as if it were your last because someday you're going to be right.”