US motorsport legend Bobby Unser, a three-time winner of the Indianapolis 500 who won the race in three different decades, has died aged 87.
A statement from the Indianapolis Motor Speedway on Monday said Unser had passed away at his home in New Mexico on Sunday.
The charismatic racing driver won the Indy 500 in 1968, 1975 and 1981, making him one of only two men to win the race in three different decades.
Unser was part of a successful racing family -- younger brother Al won the Indy 500 four times, in 1970, 1971, 1978 and 1987. Four other members of the family also raced in the Indy 500.
"When you mention icons in racing, and particularly the Indianapolis Motor Speedway, Bobby Unser was a legend," Indianapolis Motor Speedway president J. Douglas Boles said in a statement.
"He could drive, and win, in any type of car and on any type of track. And he was magical at Indy. But driving was just a piece of what made Bobby so iconic.
"His lifelong passion for promoting auto racing and his enthusiastic, no sugar-coated opinions that continued after he hung up his helmet had such a meaningful impact."
Team boss Roger Penske paid tribute to Unser -- who delivered a controversial victory in the Indy 500 to Team Penske in 1981 -- as a "true racer."
"There simply was no one quite like Bobby Unser," Penske said. "Bobby was a ferocious competitor on the track, and his larger-than-life personality made him one of the most beloved and unique racers we have ever seen.
"Beyond his many wins and accomplishments, Bobby was a true racer that raised the performance of everyone around him."
Unser's 1981 victory in the Indy 500 is regarded as one of the most controversial in the event's history.
Unser took the checkered flag on the day with Mario Andretti finishing second, only to be stripped of the title after race officials said he had passed cars illegally while exiting the pit area during a caution.
A protracted appeals process finally ended five months later with Unser being reinstated as the race winner.
The win would ultimately prove to be the last of Unser's IndyCar career, which included 35 wins and two championships.
The Indy 500 was a favourite hunting ground with Unser posting 10 top-10 finishes in the race in 19 starts.
However the 1981 controversy left him disillusioned with racing and prompted his retirement from the sport.
"Yes I am very bitter," he said at the time. "The damage has already been done... Racing has gotten old, but Indy has gotten me down. And if I were drawing a picture of my future, I'd paint Indy right out."