The Stars-and-Stripes-adorned "Captain America" chopper ridden by Peter Fonda in the classic American road movie Easy Rider will cross the auction block on October 17 and is expected to become the world's most valuable motorcycle if its estimated sale price of US$1,000,000 to US$1,200,000 is met.

Arguably the world's most famous and instantly recognizable motorcycle, the chopped Panhead Harley-Davidson played a central role in one of the American Film Institute's top 100 movies of all-time, starring alongside Peter Fonda, Dennis Hopper and a young actor in his first major role, Jack Nicholson.

The Panhead Harley began life as a Harley-Davidson FLH police bike used by the Los Angeles Police Department before being purchased second-hand and radically-modified for its film role – Harley-Davidson would not supply motorcycles for the film because of the "outlaw" motorcycle image it portrayed.

There is some conjecture as to how many "Captain America" bikes were built from Harley FLH police bikes for the film. Movie cars and motorcycles are often duplicated so that filming can continue uninterrupted in case of mechanical issues or mishap. Popular culture seems to believe it was two bikes, but Paul D'Orleans of the Vintagent blog, who has researched the chopper extensively for his upcoming book "Chopper: the Real Story," believes it was four bikes.

One (or three) of those bikes was/were stolen between the completion of filming and the release of the film, and their whereabouts are unknown. A few months ago a once-stolen Ferrari 375 sold for GBP10,753,50 (US$16,380,895) and became one of the ten most valuable cars ever sold at auction. Its redemption came after a long and bitter legal dispute that lasted 23 years. The stolen Captain America chopper(s) is/are unlikely to reappear, though it is a slim possibility. Harley-Davidsons have always been the most likely motorcycle marque to be stolen – invariably the stolen bikes are broken up for parts and that's probably what happened.

The bike to be auctioned shared filming duties with its identical siblings equally during filming, ridden by Wyatt (Fonda) and with George Hanson (Nicholson) as passenger. During filming the radically-chopped hardtail Panhead sometimes proved to be a handful to ride (if you've never ridden a chopper, it's unquestionably a triumph of form over function) and during one mishap it got so far out-of-shape that Nicholson's knees broke one of Fonda's ribs.

In addition to this bike being ridden in the film, it was the bike used (and crashed and burned) during the climactic final sequence. Following production, Fonda gave the remains of the motorcycle to fellow actor, Dan Haggerty, who helped maintain the motorcycles during filming and its provenance is assured with a letter of authenticity from Fonda. It is perhaps fortuitous that it was partially destroyed (and subsequently restored) otherwise it would no doubt have been stolen with the other(s).

Easy Rider was a low-budget film that became a cinema landmark when it was released in 1969, grossing more than US$60 million worldwide and capturing the essence of sixties angst with its drug use, counter-culture themes and a soundtrack comprised of sixties rock tracks, which has subsequently been judged by Time magazine as one of the 25 most significant film soundtracks of all-time.

Indeed, the soundtrack cost US$1,000,000 to license, almost three times the film's entire US$360,000 production budget. The global success of the film significantly contributed to the massive popularity of such anthems of the sixties as Steppenwolf's Born to be Wild, the Fraternity of Man's Don't Bogart that joint, my friend, Bob Dylan's It's Alright, Ma, I'm Only Bleeding, The Who's I Can See for Miles, Procol Harum's A Whiter Shade of Pale, The Moody Blues' Nights in White Satin, Jefferson Airplane's White Rabbit, Eric Burdon's San Franciscan Nights, Joe Cocker's With a Little Help from My Friends, Thunderclap Newman's Something in the Air and Jimi Hendrix' If 6 Was 9.

While film scores have always helped to imprint and recall visual imagery via radio, the synergistic relationship between Easy Rider's sound track and its success began an "audio-imprinting" trend, as did the subsequent rise of "new Hollywood" which the film is credited with catalyzing.

The Sixties was an era of big budget films and the independently-produced Easy Rider became one of the top three earning films of the year behind Butch Cassidy and the Sundance Kid and Midnight Cowboy.

The auctioneer (Profiles in History) press release perfectly captures the significance of the bike: "Captain America's stretched-out American-flag-adorned panhead chopper is one of the most iconic images in American film," noted Joseph M. Maddalena, President and Chief Operating Officer, Profiles in History. "The bike evokes powerful emotions even in non-bikers. It personifies the 60's, all of the good and the bad that decade brought. This is an opportunity for someone to own a pure piece of nostalgic entertainment history."

The significance of the motorcycle as babyboomer icon of the sixties suggests the bike will almost certainly become the most valuable motorcycle ever sold at auction if it meets its reserve. In 2007, the American Flag Patch worn on the back of Peter Fonda's jacket in the film sold for US$89,625 at auction.

Should the Captain America bike sell in its anticipated range, it will also become the most valuable roadgoing motorcycle ever sold.

Currently, the most valuable motorcycle ever sold at auction was a 1910 Winchester motorcycle, which sold on October 31, 2013 for US$580,000, emphasizing that provenance is very important in determining the price any object fetches at auction.

The most expensive motorcycle to ever change hands was a 1948 Vincent Black Lightning famously ridden by Rollie Free at Bonneville Salt Flats to a then record speed of a 150.313 mph (241.905 km/h) over the "flying mile" on September 13, 1948.

The "Bathing Suit Bike" was sold by elite Texan rare motorcycle agency and restoration service Harris Vincent Gallery to well-known collector Chip Connor in late 2011 for US$1,000,000.

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