Obama says he keeps a pair of Ali's gloves on display in his private study, just off the Oval Office and under the famous photograph of the young champion "roaring like a lion over fallen Sonny Listen."
Obama says in a statement that Ali "fought for what was right," stood with Martin Luther King Jr. and Nelson Mandela "when it was hard" and "spoke out when others wouldn't."
PHOTOS: Muhammad Ali through the years
Obama says even as Ali's physical powers were in decline, the boxing great "became an even more powerful force for peace and reconciliation around the world."
The president says Parkinson's disease may have "ravaged" Ali's body, but it "couldn't take the spark from his eyes."
He shook up the world, and the world's better for it. Rest in peace, Champ. pic.twitter.com/z1yM3sSLH3— President Obama (@POTUS) June 4, 2016