It was a thing of beauty: the Ali shuffle, a blur of movement that befuddled opponents and delighted fans. Years later, it morphed into a shuffling gait -- a classic sign of Parkinson's.
And the "Louisville lip" gave way to silence.
Dr. Stanley Fahn, a neurologist specializing in Parkinson's, was the first doctor to diagnose his condition. It was 1984.
"It was a slowness of movement that was his limiting factor at that time," Fahn told CBS News. "I saw immediately he had a masked face, that is, decreased expression. He had decreased blinking, and he had a typical Parkinson's tremor."
Parkinson's is most common in older adults. Ali was only 42.
"I thought some of the symptoms were too early for classic Parkinson's," Fahn said. "This was most likely going to be due to some trauma, multiple traumas to the head."
His handlers told Fahn they noticed Ali slowing down. He was not as quick as usual at the famous "Thrilla in Manila" fight against Joe Frazier in 1975 -- almost a decade earlier.
"You have slowness of movement, slows his reaction time, and that probably led to him being beaten up too much in the ring -- and that probably worsened the trauma to his brain," Fahn said.
The boxer once so fleet of foot could not sidestep his illness. But he raised awareness of Parkinson's and became a champion for others living with the disease.
No surprise. That's what a champion does.
Even as his illness progressed, Ali remained a figure of grace under pressure. He helped raise more than $100 million for the Muhammad Ali Parkinson Center in Phoenix.