Muhammad Ali, known around the world as the greatest boxer of all time, has passed away in a Phoenix, Arizona hospital. He was 74 years old. 

Multiple sources reported Ali died late Friday night (June 3) after he was checked into the hospital with respiratory issues earlier in the week.

Bob Gunnell, a spokesperson for Ali's family, confirmed his passing to NBC News, saying: "After a 32-year battle with Parkinson's disease, Muhammad Ali has passed away at the age of 74. The three-time World Heavyweight Champion boxer died this evening."

Boxers, sports writers, celebrities and more paid their respects to Ali on Twitter following news of his death.

See some of Muhammad Ali's best KOs of all time below