Lewis Hamilton and Sebastian Vettel expressed shock on Thursday as the sudden death of long-standing race director Charlie Whiting plunged Formula One into mourning on the eve of the new season.
The 66-year-old Briton, who had been at the helm since 1997 and was a pivotal figure in the sport, suffered a pulmonary embolism, or blood clot, as he prepared for Sunday's Australian Grand Prix in Melbourne.
"It is with immense sadness that I learned of Charlie's sudden passing," FIA president Jean Todt said in a statement.
"I have known Charlie Whiting for many years and he has been a great race director, a central and inimitable figure in Formula One who embodied the ethics and spirit of this fantastic sport," he said.
"Formula 1 has lost a faithful friend and a charismatic ambassador in Charlie," he added.
The popular Whiting began his F1 career in 1977 working at the Hesketh team, then in the 1980s at Bernie Ecclestone's Brabham, where he was chief mechanic during the world title successes of Nelson Piquet in 1981 and 1983.
He rose to chief engineer before becoming an integral part of organising the world championship after joining the Federation Internationale de l'Automobile in 1988.
His role included overseeing track and car safety, procedural matters on grand prix weekends and starting the race itself.
Whiting died just a day before he was scheduled to officiate at the first practice session of the season at Albert Park in Melbourne. It was not clear who would replace him.
Throughout his career, Whiting was a driving force in pushing improved safety and played a key role in the introduction of the halo, the ring-like barrier fitted over drivers' heads as protection.
"I've known Charlie since I started in 2007," said reigning world champion Hamilton, a fellow Briton. "What he did for this sport and his commitment, he really was a pillar. He was an iconic figure."
Vettel, a four-time world champion, said he saw Whiting on Wednesday and walked the first few corners of the Albert Park track with him.
"It's difficult to grasp when someone is not there anymore," he said.
"I've known him for a long time and he's been like our man, the drivers' man. You could ask him anything anytime, he was open to anyone. He was a very nice guy."
Formula one managing director Ross Brawn said he was "devastated" at the news, after knowing Whiting all his racing life.
"We worked as mechanics together, became friends and spent so much time together at race tracks across the world. I was filled with immense sadness when I heard the tragic news. I'm devastated," he said.
"It is a great loss not only for me personally but also the entire Formula 1 family, the FIA and motorsport as a whole."
Red Bull chief Christian Horner said Whiting's death would leave "a huge void in our sport".
"He was a man with great integrity who performed a difficult role in a balanced way," he said.
"At heart, he was a racer with his origins stretching back to his time at Hesketh and the early days of Brabham."
The Haas team said the "entire motorsport community is in mourning", while Renault called him "one of the pillars and leaders of the sport".
"His drive to ensure exciting, safe and fair racing was unparallelled and his passion will be sorely missed," Renault said.
Racing great Mario Andretti said the news of Whiting's death was "totally shocking".
"Charlie was a true giant in our sport and very possibly irreplaceable. RIP my friend," he said.