AP photo by Doug McSchooler / Former driver Al Unser Sr., a four-time winner of the Indianapolis 500, poses with the Borg-Warner Trophy at Indianapolis Motor Speedway in July.

This story was updated with more information at 9:10 p.m. on Dec. 10, 2021.

Al Unser, one of only four drivers to win the Indianapolis 500 a record four times, died Thursday after a long illness. He was 82.

Unser died at his home in Chama, New Mexico, with his wife Susan by his side, Indianapolis Motor Speedway announced early Friday. He had been battling cancer for 17 years.

"My heart is so saddened. My father passed away last night," Al Unser Jr., a two-time Indy 500 winner, posted on social media. "He was a Great man and even a Greater Father. Rest In Peace Dad!"

Al Sr. is the third member of one of America's most famed racing families to die in 2021. His oldest brother, three-time Indy 500 winner Bobby Unser, died in May, and Bobby Unser Jr. passed six weeks after his father.

Known as "Big Al" after his own son made a name for himself in racing, Unser is part of an elite club of four-time winners of "The Greatest Spectacle in Racing." Unser won the Indy 500 in 1970, '71, '78 and '87, and he's the only driver in history to have both a sibling and a child also win one of the biggest races in the world.

His final victory at age 47 made him the oldest winner in Indy 500 history. He dominated in his first Indy win by starting from the pole position and leading all but 10 of the 200 laps. Unser beat runner-up Mark Donohue by 32 seconds that year.

Unser led more than half of the laps in three of his Indy 500 victories, and his 644 total laps led are the most in race history. He made 27 starts in the Indy 500, which ranks third, and qualified once on the pole and five times on the front row.

Unser won three national championships in American open-wheel series competition during his career, and his total of 39 victories are sixth on the all-time list.

He and Al Jr. were the first father-son pairing at Indianapolis, and in 1985 they battled one another for the CART championship. A pass in the closing laps of the race gave Unser a fourth-place finish in the season finale at Miami's Tamiami Park road course, and it was enough for him to beat Al Jr. for the championship by a single point. He fought back tears while describing the "empty feeling" of defeating his son.

Unser also ran five NASCAR races in his career and finished in the top 10 in three of them, including fourth in the 1968 Daytona 500. He also won three times in the International Race of Champions, an all-star series that pitted the top drivers from various disciplines against each other.

Unser won the Indy car "Triple Crown" by winning all three of the 500-mile races on the 1978 schedule, at IMS, Pocono International Raceway in Long Pond, Pennsylvania, and California's Ontario Motor Speedway. He's the only driver in history to win all three of those races in the same season.

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Remembering Al Unser, four-time winner of Indianapolis 500

The Unser family combined for a record nine wins in the Indy 500. Bobby won in 1968, '75 and '81, while Al Jr. won in '92 and '94. Big Al, Bobby and Al Jr. and each won his final Indy 500 Indy 500 driving for Roger Penske.

"Al was the quiet leader of the Unser family, a tremendous competitor and one of the greatest drivers to ever race at the Indianapolis Motor Speedway," Penske said. "We were honored to help Al earn a place in history with his fourth Indy victory ... and he will always be a big part of our team. Our thoughts are with the Unser family as they mourn the loss of a man that was beloved across the racing world and beyond."

Unser earlier this year was at IMS to welcome Castroneves as the newest member of the four-time winners club. Unser achieved the feat a decade after A.J. Foyt's fourth, and Rick Mears joined the group in 1991. Castroneves won in May behind the wheel of a Penske car to become the first new member in 30 years.

"Some days the race track smiles on you, and some days you got it the other way," Unser said during the July celebration. "It's not always that you're going to think you're going to win because your chances are very slim. There's 32 other guys who want it as bad as you do."

Unser received his Baby Borg — the 18-inch replica of the Indy 500 winner's Borg-Warner Trophy that remains on site in the speedway's museum — during a celebration in May with family and friends. He was set to be honored on the 50th anniversary of his 1970 victory at Indianapolis, but the celebration was postponed because of the coronavirus pandemic.

Both Castroneves and two-time Indy 500 winner Takuma Sato lauded Unser, with Sato calling Unser's speech at the May winner's ceremony "very funny and so charming."

"I will always remember Big Al welcoming me to the speedway," Castroneves told The Associated Press on Friday. "He and Johnny Rutherford were the two helping me with my rookie orientation. He will be missed."

The youngest of four racing brothers, Unser was born in in Albuquerque in 1939 to a family of hardcore racers. His father Jerry Unser and two uncles, Louis and Joe, were also drivers. Beginning in 1926, the family began competing in the Pikes Peak International Hill Climb, an annual road race held in Colorado.

Al's oldest brother, Jerry, became the first Unser to qualify for the Indy 500 in 1958; he was killed in a crash during practice the following year.

Al began racing in 1957 when he was 18, but he competed mostly in sprint cars. He made it to Indy in 1965 driving in a car owned by Foyt and was part of a rookie class with future 500 winners Mario Andretti (1969) and Gordon Johncock ('73, '82).

"Al was one of the smartest drivers I ever raced against," Andretti said. "I often said that I wished I could have had some of his patience."

The Unser family combined for 73 career starts in the Indy 500, a number bettered only by the 76 starts by the Andretti family. The Unser participation spans Al Sr. (27 races), Bobby (19), and Al Jr. (19), as well as Johnny (five), Robby (two) and Jerry (one).

Those who knew Unser best understood the combination of humility and success is what made him a fan favorite, an admired adviser and a respected competitor.

"You help someone make their first race, and see him being one of the first four-time winners, it made me happy because he deserved it. He worked hard," said Foyt, who turns 87 next month. "He was just a super guy. He was a good race car driver, he just wouldn't brag about it."

Unser was inducted into the Indianapolis Motor Speedway Hall of Fame in 1986 and the International Motorsports Hall of Fame in 1998. His collection of trophies and cars is housed at the Unser Racing Museum in Albuquerque.

Unser was preceded in death by daughters Mary and Deborah.