- Video report by ITV News Correspondent Rachel Younger
The world of motor racing has been paying tribute to three-time Formula One world champion Niki Lauda, who has died at the age of 70.
The former racing driver "passed away peacefully", his family said on Monday, in a statement reported by the Austria Press Agency.
Four-time F1 champion Alain Prost led the tributes, saying his former teammate was a role model.
Lauda and Prost drove together for two seasons for the McLaren team in 1984-85.
"It's simple. When I started to take an interest in Formula One, I had two models: Jackie Stewart and Niki," Prost said.
"And I had the chance to spend two years by his side. These were the two most beautiful and best seasons of my career," he said.
Lauda beat Prost for the title by half a point in 1984, but the Frenchman said he never resented him.
"He taught me how to put things into perspective," Prost said.
"When I did not feel well, after a loss, he taught me how to get detached.
"He made me drink my first whisky in 1984 to take things off my mind. He taught me how to compartmentalise. That was his philosophy."
Three-time F1 champion Jackie Stewart told ITV News that Lauda joined Formula One as he was leaving.
He said: "He developed into truly one of the greatest drivers of all time."
And former British F1 driver Jonathan Palmer was just starting out in the sport in 1984 - as Lauda was winning his third title.
Palmer told ITV News that Lauda was an "amazing" driver and a "great character".
A big part of the Lauda legend was how he got back in an F1 car just 43 days after so nearly losing his life in a horror crash in 1976 where his Ferrari burst into flames in Germany.
Lauda recalled later that fear was something he just had to overcome or he'd never race again.
Britain's current world champion Lewis Hamilton tweeted that he was "struggling to believe you are gone".
Hamilton, who worked with Lauda at Mercedes, said he was a "bright light in my life".
Lauda's family said in their statement: "His unique successes as a sportsman and entrepreneur are and remain unforgettable.
"His tireless drive, his straightforwardness and his courage remain an example and standard for us all.
"Away from the public gaze, he was a loving and caring husband, father and grandfather.
"We will miss him very much."
Another British F1 champion, Damon Hill, said: "He was a remarkable individual in every way.
"I was certainly one person that looked at Niki and thought, 'I'll never be half the man he was'.
"His career was stylised and characterised by his intelligent approach.
"When he came up against Alain Prost, he knew he couldn't beat him on speed so he beat him on tactics."
Lauda was also mourned by F1, who tweeted: "Forever carried in our hearts, forever immortalised in our history.
"The motorsport community today mourns the devastating loss of a true legend."
While the McLaren Formula One team said: "All at McLaren are deeply saddened to learn that our friend, colleague and 1984 Formula 1 World Champion, Niki Lauda, has passed away.
"Niki will forever be in our hearts and enshrined in our history."
Lauda narrowly escaped death in 1976 when his Ferrari crashed at the Nurburgring in Germany and he was trapped in the wreckage as his car burst into flames.
He made a miraculous recovery despite horrific burns and finished second in the championship to James Hunt, returning to the track at the Italian Grand Prix just 43 days later.
The rivalry between the pair was later made into a film starring Daniel Bruhl as Lauda and Chris Hemsworth as Hunt in 2013.
In an Instagram post, Bruhl said on Tuesday that Lauda was the "bravest man I ever met".
He added: "He was totally unpretentious and incredibly funny. I learned a lot from him and deeply admired him."
Lauda went on to win two of his three titles as well as becoming a prominent figure in the aviation industry.
In 1979, he left the sport to concentrate on setting up his airline, Lauda Air.
He briefly returned to racing following an offer from McLaren, winning the F1 drivers’ championship for a third time in 1984, before retiring for good the following year.
Lauda founded a new airline, Niki, in 2003.
In later years, he served as the non-executive chairman of the Mercedes team and formed a close bond with driver Lewis Hamilton, who joined the team in 2013.
Mercedes F1 team principal Toto Wolff said Lauda "combined heroism, humanity and honesty inside and outside the cockpit".
He added: "His passing leaves a void in Formula One. We haven't just lost a hero who staged the most remarkable comeback ever seen, but also a man who brought precious clarity and candor to modern Formula One.
"He will be greatly missed as our voice of common sense."
Over the past few decades, Lauda twice underwent kidney transplants, receiving an organ donated by his brother in 1997 and a kidney donated by his girlfriend in 2005.
In August last year, he underwent a lung transplant that the Vienna General Hospital said was made necessary by a “serious lung illness.”
He was released for rehabilitation nearly four months later but was back in hospital in January with influenza.
A doctor who oversaw Lauda's lung transplant last year said the motor racing legend had been in poor shape for some time.
Walter Klepetko of Vienna General Hospital told the Austria Press Agency on Tuesday "it was a long process at the end of which the patient passed away".
He added "Niki Lauda fought. He was a great man. But it had been clear for some time that we could not get him back on the 'racing track.'"
Lauda is survived by his second wife Birgit, and his children, Max, Mia, Mathias, Lukas and Christoph.