Muhammad Ali died Friday at age 74, according to a statement from the family. He was hospitalized in the Phoenix area with respiratory problems earlier this week, and his children had flown in from around the country.
"It's a sad day for life, man. I loved Muhammad Ali, he was my friend. Ali will never die," Don King, who promoted some of Ali's biggest fights, told The Associated Press early Saturday. "Like Martin Luther King his spirit will live on, he stood for the world."
A funeral will be held in his hometown of Louisville, Kentucky. The city plans a memorial service Saturday.
Louisville Mayor Greg Fischer ordered flags lowered to half-staff to honor Ali.
"The values of hard work, conviction and compassion that Muhammad Ali developed while growing up in Louisville helped him become a global icon," Fischer said. "As a boxer, he became The Greatest, though his most lasting victories happened outside the ring."
With a wit as sharp as the punches he used to "whup" opponents, Ali dominated sports for two decades before time and Parkinson's disease, triggered by thousands of blows to the head, ravaged his magnificent body, muted his majestic voice and ended his storied career in 1981.