Mario Andretti silently stewed as Bobby Unser celebrated winning the 1981 Indianapolis 500.

Andretti had finished second that day as Unser took over the lead when Gordon Johncock blew an engine with less than 10 laps to go. Unser went on to win for a third time with a margin of victory of 5.18 seconds over Andretti, who wasn't done by a long shot, not after Unser exited pit road under caution and passed 14 cars.

Adamant that no passing under yellow was allowed, Andretti filed a protest before the night was over. After an overnight review, Andretti was declared the winner. Unser's team filed an appeal, which was initially denied. It wasn't until October — five torturous months after the race — that Unser was reinstated as the victor.

"There were several rivalries that happened over the years, but probably Andretti and Bobby Unser when they couldn't decide the winner was the best," said Parnelli Jones, who won the race in 1963.

In the lead-up to the 100th running of the "The Greatest Spectacle in Racing," The Associated Press interviewed the 27 living race winners on topics ranging from the best driver to greatest tradition. When it came to deciding the greatest rivalry, A.J. Foyt, Andretti and Unser received the most attention in the AP survey.

The clear winner was A.J. Foyt versus Andretti. But Foyt versus the entire field wasn't far behind.

"The one I paid attention to was A.J. and myself, I lived it," said Andretti.

Every generation of driver has a Foyt and Andretti story, and all considered racing and beating Foyt their ultimate barometer.

"Foyt and pretty much anyone who he thought could stop him winning," said Dario Franchitti. "It seems to me that when A.J. went racing, he went to war. He had respect for his rivals, but they were the enemy. The rivalries are still there 50 years later."

Added Scott Dixon on the Foyt-Andretti rivalry: "I think the media made the most of it," he said, "but the rivalry was so great because they were fighting it out every weekend with no filter."

When it comes to Indianapolis, Foyt gets the nod over Andretti. "Super Tex" was the first four-time winner and fearless competitor. When he won his final 500, in 1977, a decade after his third victory, Foyt was 42 and his prize money that day made him the first driver at Indianapolis Motor Speedway to top $1 million in career earnings.

"The greatest rivalry had to be A.J. Foyt against anyone else," said Bobby Rahal. "Super Tex was the yardstick in the '60s and 70's, and no matter who else was there, the man to beat was A.J."

Johnny Rutherford felt while Andretti and Unser were tough foes, Foyt viewed all competitors with the same intensity and desire to beat them.

"Just about anybody in the field and A.J. Foyt," Rutherford said. "A lot of people don't understand A.J. He's intense. He's a racer. He doesn't want to lose and he does just about anything he can to win. There were some monumental battles."

And just who did Foyt consider his greatest rival? Good luck finding out.

"I know who I didn't care for and who didn't care for me," Foyt said this month, "but I'd rather not say anything else."

A current generation doesn't think the rivalries are the same. Most of today's IndyCar drivers are friends, they go to dinner together, exchange well-wishes on Twitter and quickly resolve any disagreements. It's the mark of a different time, said Buddy Rice, who remembers Foyt's days of dominance.

"You're going to have to go back to the '60s and '70s and '80s for good rivalries, when people were characters and everyone had personality," Rice said. "Those guys back then — their charisma, doing their own thing — a lot of those guys did what they wanted to do and how they wanted to do it, and that's why everybody followed it and was so into it. Those are some really good times, a really good era."

But, there may be still one good rivalry remaining, noted Sam Hornish Jr. He beat both Marco Andretti and Michael Andretti to win the 2006 Indianapolis 500 and continue the frustrating run of close-calls for the Andretti family. Mario Andretti's victory in 1969 stands as the only one for a family that has chased its curse around the speedway for decades.

That in itself is a rivalry, said Hornish.

"Regardless of the Unsers and the Andrettis and Foyt versus everybody else — a lot of those races came down to one guy against one other, but there's nothing that's been more talked about since the '60s than the Andrettis trying to get more than one victory there," Hornish said. "The one thing I remember most, when we were at the banquet the next night (after I won), Mario walked up to me and shook my hand and said, 'You're a bad man, Sam Hornish.' And I was like, 'Thank you.'

"That race means the world to them."