Mr Johnson said Palmer was admitted to hospital on Thursday for cardiovascular work and weakened over the last few days.

At ease with both presidents and the golfing public and on a first-name basis with both, Palmer ranked among the most important figures in golf history, and it went well beyond his seven major championships and 62 PGA Tour wins.

His good looks, devilish grin and go-for-broke manner made the elite sport appealing to one and all. And it helped that he arrived about the same time as television moved into most households, a perfect fit that sent golf to unprecedented popularity.

Tiger Woods tweeted: "Thanks Arnold for your friendship, counsel and a lot of laughs," . "Your philanthropy and humility are part of your legend. It's hard to imagine golf without you or anyone more important to the game than the King."

Jack Nicklaus, a great rival of Palmer, said: "He was one of my best friends, closest friends, and he was for a long, long time. I will miss him greatly.

"Arnold transcended the game of golf. He was more than a golfer or even great golfer. He was an icon. He was a legend. Arnold was someone who was a pioneer in his sport.

"We were great competitors, who loved competing against each other, but we were always great friends along the way. Arnold always had my back, and I had his. We were always there for each other. That never changed. He was the king of our sport and always will be."

Beyond his golf, Palmer was a pioneer in sports marketing, paving the way for scores of other athletes to reap in millions from endorsements. Some four decades after his last PGA Tour win, he ranked among the highest earners in golf.

On the golf course, Palmer was an icon not for how often he won, but the way he did it.

He would hitch up his trousers, drop a cigarette and attack the flags. With powerful hands wrapped around the golf club, Palmer would slash at the ball with all of his might, then twist his muscular neck and squint to see where it went.

He left behind a gallery known as "Arnie's Army", which began at Augusta National with a small group of soldiers from nearby Fort Hood, and grew to include a legion of fans from every corner of the world.

Palmer stopped playing the Masters in 2004 and hit the ceremonial tee shot every year until 2016, when age began to take a toll and he struggled with his balance.

It was Palmer who gave golf the modern version of the Grand Slam - winning all four professional majors in one year. He came up with the idea after winning the Masters and US Open in 1960.

He was runner-up at the British Open, later calling it one of the biggest disappointments of his career. But his appearance alone invigorated the tournament, which Americans had been ignoring for years.

He never like being referred to as "the King", but the name stuck.

"It was back in the early 60s. I was playing pretty good, winning a lot of tournaments, and someone gave a speech and referred to me as 'the King'," Palmer said in 2011.

"I don't bask in it. I don't relish it. I tried for a long time to stop that and ... there was no point."

He was equally successful with golf course design, a wine collection, and apparel that included his famous logo of an umbrella. He bought the Bay Hill Club & Lodge upon making his winter home in Orlando, Florida, and in 2007 the PGA Tour changed the name of the tournament to the Arnold Palmer Invitational.

The combination of iced tea and lemonade is known as an "Arnold Palmer".

Palmer was born in Latrobe, Pennsylvania, the oldest of four children. His father Deacon became the greenskeeper at Latrobe Country Club in 1921 and the club pro in 1933.

He had two loves as a boy - strapping on his holster with toy guns to play cowboys and Indians, and playing golf. It was on the golf course that Palmer grew to become so strong, with barrel arms and hands of iron.

"When I was six years old, my father put me on a steel-wheeled tractor," he recalled. "I had to stand up to turn the wheel. That's one thing made me strong. The other thing was I pushed mowers. In those days, there were no motors on anything except the tractor. The mowers to cut greens with, you pushed."

Palmer's image was everywhere, from motor oil to ketchup to financial services companies.

Even as late as 2011, nearly 40 years after his last PGA Tour win, he was number three on Golf Digest's list of top earners at 36 million dollars (£27.7m) a year, trailing only Woods and Phil Mickelson.

Palmer's other love was aviation. He piloted his first aircraft in 1956, and 10 years later had a licence to fly jets that now are the standard mode of transportation for so many top players, even though the majority of them are merely passengers.

He set a record in 1976 when he circumnavigated the globe in 57 hours, 25 minutes and 42 seconds in a Lear 36. He continued flying his Cessna Citation 10 until he failed to renew his licence at 81, just short of 20,000 hours in the cockpit.

Palmer's first wife, Winning, died in 1999. They had two daughters, and grandson Sam Saunders plays on the PGA Tour. Palmer married Kathleen (Kit) Gawthrop in 2005.

US president Barack Obama tweeted: "Here's to The King who was as extraordinary on the links as he was generous to others. Thanks for the memories, Arnold."

Mr Palmer's one-time rival Gary Player said: "Arnold oozed with charisma, was a great icon and did so much for the game."

Rory McIlroy, one of the top golfers in the world today, told the BBC: "Arnold, especially at the time in the 60s and 70s, really brought the game to the masses.

"I don't think anyone in any sport has left a legacy like Arnold Palmer has.

"I was able to spend a little bit of time with him over the last couple of years and I'll always cherish that and remember that. He's a very good man, a very generous man, and he'll live long in the memory of a lot of people."