BOXING LEGEND MUHAMMAD ALI DIES AT 74.

Former heavyweight boxing champion Muhammad Ali, the most important, complex and polarizing athlete of our time, died Friday night at an Arizona hospital. He was 74. He had suffered for decades from Parkinson's disease, a progressive neurological disorder, and was being treated in the hospital in recent days for a respiratory issue.

"After a 32-year battle with Parkinson's disease, Muhammad Ali has passed away. . . . The three-time World Heavyweight Champion boxer died this evening," Bob Gunnell, a family spokesman, told NBC News.

Ali had been hospitalized in the Phoenix area this week, and reports said he was fighting respiratory issues that were complicated by the Parkinson’s that he was diagnosed with in the 1980s

Ali had been hospitalized several times in recent years, most recently in early 2015 when he was treated for a severe urinary tract infection initially diagnosed as pneumonia.

Ali looked increasingly frail in public appearances, including April 9 when he wore sunglasses and was hunched over at the annual Celebrity Fight Night dinner in Phoenix, which raises funds for treatment of Parkinson’s.

His last formal public appearance before that was in October when he appeared at the Sports Illustrated Tribute to Muhammad Ali at The Muhammad Ali Center in his hometown of Louisville, Kentucky, along with former opponents George Foreman and Larry Holmes.

Ali suffered from Parkinson’s for three decades, most famously trembling badly while lighting the Olympic torch in 1996 in Atlanta. Despite the disease he kept up a busy appearance schedule until recently, though he had not spoken in public for years.

Doctors say the Parkinson’s likely was caused by the thousands of punches Ali took during a career in which he traveled the world for big fights.

Ali burst onto the scene as Cassius Clay, winning an Olympic gold medal in 1960. On Feb. 25, 1964, he stopped heavyweight champ Sonny Liston in Miami Beach, Fla., to capture the crown.

In short order, Clay joined the Nation of Islam and changed his name to Muhammad Ali, and became a heavyweight for causes outside the ring.

His boxing career was derailed in 1967 when Ali was stripped of his title for refusing to be drafted into the military, citing his religious beliefs and his opposition to the Vietnam War. Convicted of draft evasion on June 20 of that year, he was sentenced to five years in prison. Ali remained free on bond and fought for his freedom.

Ali was sidelined for almost four years in his prime before he returned to the ring in 1970, and the U.S. Supreme Court overturned his conviction the following year. That set the stage for a remarkable career outside the ring as a humanitarian.

Ali had three legendary fights with Joe Frazier, losing the first by decision and winning the next two.

He stunned George Foreman in the “Rumble in the Jungle” in 1974 to regain the heavyweight championship, becoming the first person to do so.

Ali finished with a career record of 56-5 with 37 knockouts.

His impact around the globe was greater, as he took on iconic status and became the best-known person on the planet.

Ali spent the final years of his life in the Phoenix area with his fourth wife, Lonnie, whom he married in 1986.