Nigel Mansell has hailed Ayrton Senna as his "toughest rival" and a driver who "stood out" even amongst great drivers.
May 1st marks 20 years since triple World Champion Senna was killed when he crashed while leading the 1994 San Marino Grand Prix.
His death, which came a day after Roland Ratzenberger died during the Imola weekend's qualifying, sent shock waves through the motorsport world.
On Thursday, the Imola circuit will open its doors to the public in celebration of Senna's life.
Remembering his former rival, Mansell told BBC Sport: "Ayrton was our toughest rival.
"He would leave no stone unturned to get the utmost out of his car and his team.
"In the 1980s, I was blessed to drive against so many great drivers but Ayrton certainly stood out most among them."
The duo, though, had an intense rivalry with Senna winning three World titles while Mansell claimed the crown in 1992.
"In the beginning, we were great enemies," said Mansell. "He wanted to win at all cost with everybody, so we knocked heads quite a lot."
Remembering their tussle at the 1987 Belgian Grand Prix, in which they crashed, the Brit said: "Ayrton could intimidate pretty much every driver on the grid but he realised then I would not cave in and he would have to readdress his psyche towards me.
"We went on to have many incredible races, where we didn't knock each other off. It was just good, hard, clean racing.
"And as the years ticked on, we developed a healthy respect and understanding for each other and became friends."
Others have joined Mansell in paying tribute with Sir Frank Williams, for whom Senna was racing when he died, saying there was more to the driver than racing.
"Ayrton knew what he wanted and he knew of the various people inside the company who could deliver, and he went after those guys and got them onside," he revealed.
"He was certainly on his way to becoming a president of Brazil. He had politics in mind, and if he had done so he would probably have walked it."
Meanwhile, McLaren team boss Ron Dennis told BBC Radio 5 live: "He lived for the sport. When people do that, they sacrifice everything to be the best at it.
"He understood what was needed. He had the fitness, the right mental approach, the right skills and the right level of passion."
In remembrance, McLaren released a specially commissioned short film that commemorates Formula 1's most enduring icon.