Legendary trainer Angelo Dundee has died in Florida, aged 90.
Dundee, famous for working alongside Muhammad Ali for 20 years, is reported to have had a heart attack after being taken to hospital with a blood clot.
He guided Ali through his greatest fights, including the "The Rumble in the Jungle" with George Foreman.
His son, Jimmy Dundee, said: "Thankfully, the whole family was with him. We have lost a great man. My dad led a wonderful life."
While Dundee's name was synonymous with Ali's, he worked with 14 further world champions, including Sugar Ray Leonard, George Foreman and Jimmy Ellis, during a distinguished career.
But it was his partnership with Ali which became one of the most successful in boxing history.
Dundee, born in Philadelphia, teamed up with Ali after his Olympic gold medal success in Rome in 1960 and guided him to his first heavyweight title, against Sonny Liston in 1964.
He helped Ali to two further titles, travelling to Zaire for his fighter's memorable victory over Foreman and to the Philippines in 1974 for the "The Thrilla in Manila" against Joe Frazier in 1975.
Dundee was instrumental in Ali's victory over Henry Cooper in London in 1963. Ali - then called Cassius Clay - was knocked down by Cooper but was saved by the bell.
The trainer then made a tear in one of his fighter's gloves, delaying the start of the next round and allowing Ali to regain his senses. He went on to win the next round and the fight.
Dundee was always there for his protegee: when he joined the Black Muslims and became Muhammad Ali and when he defied the draft at the height of the Vietnam war, losing three-and-a-half years from his career.
Dundee gave him the nickname 'The Louisville Lip', and Ali wrote in the forward to Dundee's book: "Through all those days of controversy, and the many that followed, Angelo never got involved.
"He let me be exactly who I wanted to be, and he was loyal. That is the reason I love Angelo."
Dundee trained Leonard for many of his biggest fights, including bouts against Wilfred Benitez, Roberto Duran and Thomas Hearns, when he famously shouted, "You're blowing it, son. You're blowing it" to inspire his charge to victory by knockout.
Dundee was inducted into the International Boxing Hall of Fame in 1994 and attended Ali's 70th birthday party last month.
Promoter Bob Arum said he had been planning to bring Dundee to Las Vegas on 18 February for a charity gala headlined by Ali.
"He was wonderful. He was the whole package," Arum said. "Angelo was the greatest motivator of all time. No matter how bad things were, Angelo always put a positive spin on them. That's what Ali loved so much about him."
And he added: "Ali was this unbelievable figure, and a guy who symbolised an entire era of American culture and was idolised around the world.
"And through all those times, the person at his side was Dundee. For that, he will always be remembered."
American sportswriter Bert Sugar, ghostwriter of Dundee's autobiography, said: "He did things so subtly and he did them because he was Angelo Dundee and he was investing himself in his fighters.
"He would teach Ali how to do things and let Ali think it was his idea. He would finish Ali's poems for him when Ali couldn't come up with a line."
Britain's former WBA heavyweight champion David Haye tweeted: "R.I.P. Angelo Dundee. The Greatest Coach ever. I had the pleasure of spending time with him in Miami last year. What a true gentleman."
Dundee died surrounded by his family. "It was the way he wanted to go," Jimmy Dundee said. "He did everything he wanted to do.
"He was coming along good yesterday [Tuesday] and then he started to have breathing problems. My wife was with him at the time, thank God, and called and said he can't breathe.
"We all got over there. All the grandkids were there. He didn't want to go slowly."