The iconic boxer reached out to Fox in 2000 after the actor revealed that he too was battling the incurable neurological condition. In an interview with ABC News today, Fox said he locked himself in the bathroom to avoid any distraction from his kids and finally mustered up the courage to call Ali back.
"I'm in the bathroom talking to Muhammad Ali. He didn't say much. He just said, "With you in this fight, we can win,'" Fox told ABC News. "I cried."
The two met in person a few months later, and they teamed up to raise awareness for Parkinson’s. They also formed a close friendship that lasted throughout the rest of Ali's life. The legendary boxer and global humanitarian died Friday night at an Arizona hospital, after a long fight with the disease.
Fox tweeted a photo of him with Ali Saturday morning in the hours after his death with the caption, “Ali, the G-O-A-T. A giant, an inspiration, a man of peace, a warrior for the cure. Thank you.”
Fox and Ali appeared together in Parkinson's PSAs, at fundraisers and even at a Senate subcommittee hearing in May 2002 to lobby lawmakers on funding research for a cure.
Ali's wife Yolanda "Lonnie" Williams served on the board of directors of the Michael J. Fox Foundation for Parkinson's Research from 2001 to 2004. A few years later, the couple was appointed to the foundation's founder's council.
"He was really committed to finding an answer to this disease, as he was to finding answers to strife in the world and wars and conflict and all kinds of things," Fox said today. "He was a very complex man and a very special man."
The actor said he looked up to Ali in more ways than one.
"His standard principles, his defiances, his artistry, his brilliance, his guts and his valiant fight with Parkinson’s," he said. "The fact that I had that to relate to as well as the other influences he had just by being him."
Fox said he "felt conflicted" after learning of Ali's passing. On one hand, he was sad for Ali's family and regretted that he didn't get a chance to speak to his friend once more.
"At the same time, I was somewhat relieved for him that he was no longer battling this," he told ABC News today. "It's a sad day but it's great to think about him as much as we have today, because he really deserves it."
ABC News' Tom Kelly contributed to this report.