One of the most famous motorcycles in movie history is set to be auctioned next month with a pre-sale estimate of up to half a million dollars – and it could prove as controversial as the counterculture film that made it a star.

The bike, which will be sold by Texas auction house Dan Kruse Classics, is claimed to be the actual Harley-Davidson chopper, known as Captain America, that was ridden by Peter Fonda in 1969’s Easy Rider. It will be offered with a certificate of authenticity from restorer Gary Graham, confirming that he rebuilt the machine during the mid 1990s for the late Grizzly Adams star Dan Haggerty, who ended up giving it to Graham as repayment for a loan. Haggerty had a small part in Easy Rider and served as its “motorcycle wrangler”, so Fonda is said to have gifted him the bike in a wrecked state following a fireball crash that marks the film’s closing scene.

Once restored, Captain America was displayed at the Iowa State Fair, where it was seen by thousands – after which it was consigned to a 1996 Kruse auction and bought for $63,500 by Texas realtor and collector Gordon Granger, whose death has prompted this year’s 5 June sale.

But in October 2014, the Hollywood memorabilia auctioneer Profiles in History sold another Captain America for $1.35m on behalf of Los Angeles realtor Michael Eisenberg. The sale was given credence by Haggerty, who publicly announced that it was the true bike, saying documents he had previously signed to authenticate the Granger bike were false. Fonda tried to block the sale in the belief that Eisenberg’s was, in fact, a replica.

The chances of establishing the genuine machine diminished with the deaths of Haggerty in 2016 and both Granger and Fonda in 2019 – but auction-house spokesperson Tiffany Kruse stated unequivocally on Thursday night: “The motorcycle we are selling is the crash bike from the movie Easy Rider.”

Dennis Hopper (left) and Peter Fonda – astride Captain America – in Easy Rider (1969)

Regardless of whether it is right or wrong, the bike will undoubtedly attract strong bidding. The bike has achieved cult status via the film, which stars Fonda as Wyatt and Dennis Hopper as Billy, a pair of hippie outlaws heading to New Orleans for Mardi Gras with the proceeds of a drug deal hidden inside a plastic tube stuffed into Captain America’s fuel tank. Along the way, they pick up drunken lawyer George Hanson (Jack Nicholson) who travels on the back of the bike wearing a cream suit and gold football helmet – and ends up being clubbed to death in his sleep by a group of disapproving locals. Wyatt and Billy continue to Mardi Gras, where they experience a bad LSD trip, before moving on the following morning – only to both be shot and killed by a redneck in a passing pick-up truck.

Easy Rider grossed $60m against a filming budget of around $400,000, making it the fourth most successful movie of 1969. But while it helped to make stars of Fonda, Hopper and Nicholson, the people who created the most vital element of the film – the motorcycles – have been almost entirely overlooked. Fonda, who wrote, produced and financed the film, was unable to persuade Harley-Davidson to provide motorcycles, so he bought four ex-police Harley Hydra-Glides at auction and gave them to a team of Los Angeles-based custom-motorcycle builders to turn into choppers. The team, led by Benny Hardy and parts supplier Cliff Vaughs, built two identical Captain Americas and two identical Billy bikes.

Both Billy bikes and one Captain America were stolen and, so the story goes, broken up for parts before Easy Rider was released, leaving the Captain America that crashed and burned in the closing sequence as the film’s only two-wheeled survivor.

Or was it?