The death of "irreplaceable" Charlie Whiting has cast a shadow over the season-opening Australian Grand Prix in Melbourne.
Whiting, who carried out a wide range of duties as the FIA Formula One race director, died on Thursday from a pulmonary embolism in the southern Australian city where he was due to work this weekend.
News of the Briton's death filtered through the paddock at Albert Park on the eve of Friday's first practice session, with seminal figures from motorsport among those paying tribute.
Reigning world champion Lewis Hamilton said Whiting was an "iconic figure in the sport".
He added: "What he did for the sport and his commitment, he really was a pillar.
"I've known Charlie since I started in 2007... what he did for the sport, his commitment, he really was an iconic figure."
Four-time world champion Sebastian Vettel said he only spoke to Whiting on Wednesday.
He said: "You could ask anything at any time, his door was always open.
"He was a racer, he was just a very nice guy."
Christian Horner, team principal at Red Bull Racing, said Whiting was a man with "great integrity" and "performed a difficult role in a balanced way".
He added: "Charlie has played a key role in this sport and has been the referee and voice of reason as Race Director for many years.
"At heart, he was a racer with his origins stretching back to his time at Hesketh and the early days of Brabham.
"Charlie was a great man who will be sadly missed by the entire Formula 1 paddock and the wider motorsport community."
Former world champion Mario Andretti said Whiting was "very possibly irreplaceable".
He tweeted: "Totally shocking news of Charlie Whiting's passing. Charlie was a true Giant in our sport and very possibly irreplaceable. Sincere condolences to his family and everyone who appreciated this man. RIPmyfriend."
Several Formula One teams also paid tribute to Whiting after news of his death broke.
Renault described him as "one of the pillars and leaders of the sport".
"His drive to ensure exciting, safe and fair racing was unparalleled and his passion will be sorely missed," Renault added.
McLaren driver Carlos Sainz added: "I always enjoyed a racing discussion with one of the most outstanding professionals in our sport. He will be very missed."
Valtteri Bottas, teammate of Lewis Hamilton for Mercedes, tweeted: "Very sad and surreal news ahead the Australian GP. Can't believe it.. My thoughts are with the family and friends. He's done so much for the sport we love. Rest in peace Charlie."
British racing driver George Russell, who competes for Williams, said he was "deeply saddened" by the news.
He tweeted: "Such a huge figure in the world of motorsport. All of my thoughts are with his family and his many friends right now. We'll all miss him very much."
Ferrari driver Charles Leclerc said: "Horrible news from Melbourne. All my thoughts goes to Charlie's family. The motorsport world will miss you. R.I.P."
