Thor, Matt Damon and the return of star power to the Indianapolis 500

Chris Hemsworth was the Honorary Starter at the 2018 Indianapolis 500. Adam Lacy/Icon Sportswire

"What's my goal with the green flag?" Chris Hemsworth said one year ago, repeating a question shouted by a sweaty race fan pressed against the fence that lines the legendarily long front-stretch grandstand of the Indianapolis Motor Speedway. "Same as with my hammer," the actor known as Thor answered. "I hope I am worthy enough to hold it ... and not, you know, drop it into the middle of the Indianapolis 500."

Moments later, as the field of 33 race cars roared by beneath him, Hemsworth proved he was indeed worthy of the task. He flicked his wrist just as he'd been instructed and whipped the green cloth firmly -- and safely -- to start the 102nd running of the Greatest Spectacle in Racing. That same day, his latest film, "Avengers: Infinity War," was No. 1 at the box office on its way to making $2 billion, and his Tag Heuer watch, the real reason he was there, was shined up and easy for any potential customers to spot as he gripped the flag's handle.

So yes, Chris Hemsworth was plenty worthy of his assignment as the honorary starter of the 2018 Indianapolis 500. So are his 2019 successors, the just-revealed Academy Award-winning duo of Matt Damon and Christian Bale. They will wave dual flags. They will also be promoting a movie, this fall's "Ford v. Ferrari" about the historic 1966 24 Hours of Le Mans.

Worthy of the task. Worthy of promotional excellence. Worthy of making folks swoon as they walk through Gasoline Alley. The same as those who occupied the Indianapolis Motor Speedway flagstand long before them or Hemsworth.

"To me, that is one of the most exciting parts of the month of May at Indy: seeing all of the famous people who show up," confesses 1969 Indy 500 winner Mario Andretti, who is just as famous as the famous people he is so excited to see. "As a driver, you get so caught up in getting ready for the race and fine-tuning that race car that you might not even enjoy Indy. Then, on race morning, Jack Nicholson walks by and says, 'Hi, Mario,' and you think to yourself, 'OK, wow! This must be a big deal here today!'"

Over the past decade, the green flag has been waved by Nicholson, Jake Gyllenhaal, Chris Pine and Patrick Dempsey. On the track below them, the honorary pace car has been driven by Jay Leno, Morgan Freeman, Jeffrey Dean Morgan and Dempsey (Dr. McDreamy is also a professional sports car driver). Meanwhile, the national anthem has been performed by Kelly Clarkson (back this year for the third time), Steven Tyler, Darius Rucker and ... wait for it ... David Hasselhoff. Race team owners have included Gene Hackman, Paul Newman and David Letterman. In 2010, the entire Kardashian/Jenner family was on the grid because a race car carried sponsorship from their endorsed diet regimen.

None of this takes into account the random celebrities who attend for unofficial reasons.

"Before every race, the last thing you always do is go to the bathroom, right?" asks three-time Indy 500 winner Bobby Unser. "Well, one year we all ran into the garage and did that, and as we're running back out, my brother [four-time 500 champion Al Unser Sr.] says to me, 'I think I just saw Bob Hope in the bathroom. Is he here today?' And as he said it, I pointed and said, 'Well, hell, I think that's Dinah Shore. Let's go ask her.'"

The first over-the-top-gigantic movie star to grace the Brickyard was Clark Gable. The Oscar-winning legend came to Speedway, Indiana, in 1947 to little fanfare. In fact, there's only one known photo of his visit in the IMS archives. When he returned three years later, not only were cameras constantly trained on the "Gone with the Wind" star, but he also brought plenty of cameras of his own, shooting a film about an Indy 500 racer and his struggles with love titled "To Please a Lady." When asked if he was planning to turn a lap around the 2.5-mile rectangle for real, he replied, "If I do, it won't be a very fast one."

The film hit theaters that fall. On the other side of the planet, a 10-year old Italian boy saw the movie and fell in love with the Indy 500. His name was Mario Andretti.

Thanks in no small part to Gable, Hollywood went all-in on Indy as a promotional tool during the 1950s. It was good business to have the newsreels that ran before feature films packed with footage of a studio's stars hanging out with racing stars when Indy 500 highlights were shown. Gary Cooper and Jimmy Stewart looking manly as they posed alongside roadsters on the grid. Dean Martin and Jerry Lewis laughing it up with grease monkeys in Gasoline Alley. Roy Rogers, Hollywood's most famous horseman, asking racers about horsepower.

In 1958, an up-and-coming young actress named Shirley MacLaine was in Victory Lane when Jimmy Bryan rolled in following the biggest win of his life. By MacLaine's own admission, she really enjoyed the gig as the center of attention during both the prerace drivers meeting and the postrace celebration. The Indianapolis Star wrote that as MacLaine presented Bryan with the Borg-Warner Trophy, she was required to give him only one kiss but went for a second smooch and then asked for a third. The paper said Bryan replied, "Certainly, if you don't mind getting your face dirty."

"That was just standard operating procedure for the movie studios: to send an actress to pose with the Indianapolis 500 champion in the winner's circle," Indianapolis Motor Speedway historian Donald Davidson said a year ago during Hemsworth's appearance, speaking of a practice that he says ran from 1947 through the end of the 1950s. "After that, this just became a must-do for celebrities, from movies to television, recording artists, sports stars."

Davidson mentioned General Chuck Yeager, the first man to break the sound barrier, who drove the pace car twice in 1986 and '88, during a time when that job was still given primarily to those with real racing experience. "I think I qualified," Yeager quips now. Davidson has always loved the symmetry of Yeager's appearances then paired with Indy's first celebrity pace car driver -- not to mention first woman given any official role at the Indy -- Amelia Earhart as "honorary referee" in 1935.

But after the heady days of James Garner, Johnny Carson, Jack Benny and Walter Cronkite, the star power waned in the late 1990s as American open-wheel racing ripped itself apart from the inside. Yes, there were big names (Ali! Michael Douglas! Guy Fieri ... ?!), but there wasn't the sheer volume of superstars that there had been during Indy's heyday.

Now, that has changed. Even the crustiest old Indy 500 curmudgeon has to admit that the buzz around the Brickyard over the past decade has increased at Pole Day-worthy speeds. Attendance numbers and the traffic that comes with them are a testament to that.

But in perhaps the most American sentence one could possibly write, the health of an event as it relates to the nation's sport consciousness is evident in how many famous people show up. At the Indianapolis 500, they are once again rolling in by the limo-full, waving flags, driving pace cars, taking selfies and thumbing 200 mph rides with legends.

"In IndyCar racing, we have spent so much time over the last 20 years talking and worrying about, have we ruined this? Can we get it all back to where it used to be?" says Tony Kanaan, who hopes to make his 18th Indy 500 start next weekend and earn his second win. "Well, a few years ago, I remember seeing Lady Gaga go by me in a fire suit on her way to get into a two-seater IndyCar with Mario. I thought to myself, 'Well, we must be doing something right again.'"