Even on its release, 40 years ago this week, Raiders Of The Lost Ark was already old hat. Directed by Mr Steven Spielberg and based on a story by Messrs George Lucas and Philip Kaufman, it took the themes and format of the B-movies and serials of their childhoods and ran with them – with a rolling boulder in hot pursuit. Set in the 1930s, when men in headgear was the norm and the only things archaeologists had to worry about were Nazis (thank goodness those guys aren’t around anymore) and snakes (“Why did it have to be snakes?”), an old-fashioned sense of adventure (and style) was hardwired into the film. But for all the antiquities that Indiana Jones went in search of, that old hat might be his greatest find.

The film’s costume designer Ms Deborah Nadoolman Landis had previously outfitted The Blues Brothers, and went on to dress Mr Michael Jackson for Thriller and earn an Oscar nomination for Mr Eddie Murphy’s regal attire in Coming To America, so it’s safe to assume she knew a stylish chapeau when she saw one. But far more was expected of Indiana Jones’ hat. It had to be something that the film’s cinematographers could use as a visual shorthand for its wearer. In short: iconic. “I had to have a hat that, if you saw it in silhouette, would be immediately recognisable,” Landis has said of the task she was set.

Initially, Spielberg presented Landis with a crude sketch of a 1930s hero in a fedora, brown jacket and boots, itself drawing heavily from cinematic references such as Mr Humphrey Bogart in 1948’s The Treasure Of The Sierra Madre. Landis in turn assembled dozens of hats for the film’s lead Mr Harrison Ford – who only signed on after contract issues forced Mr Tom Selleck to turn the role down – to try on. With Landis looking over Ford’s shoulder into a dress mirror, the pair settled on the style that worked best for the actor.

A tall stovepipe model pulled from Herbert Johnson’s Australian lines, the Poet had been handcrafted by the revered London hatmaker since the 1890s. Originally fashioned from rabbit pelt – although the version used for 2008’s Kingdom Of The Crystal Skull was a replica made from beaver hide; read into that what you will – Dr Jones’ trademark fedora had a pinched box crown, asymmetrical brim and slanting crease. The hat worn by Ford in the films features a thinner ribbon than standard, making the crown appear taller, and a slightly shaved brim, snapped down and shaped into an ovoid to allow for better framing on screen.

For added authenticity, Landis deliberately rubbed earth into the sable skin to give the impression of wear and tear. (“It’s not the years, honey. It’s the mileage,” as Indiana puts it.) The image of the costume designer figuring out just the right amount of soiling is somehow reminiscent of Indy himself guesstimating a bag of sand against the weight of a golden idol.

Landis’ effort certainly pulled off. From Raider’s opening credits, the hat is the first thing you see of the man, cropped behind the title. It sets the tone in the vague South American jungle, actually shot in Hawaii, casting its shadow across the opening scene’s cavernous temple and later the wall of a Nepalese bar. By the sequel, 1984’s Temple Of Doom, the significance of the hat to Indy’s identity is not lost, the hero risking a crushed arm to retrieve it from a falling door. Come the third film in the series, 1989’s The Last Crusade, the fedora is gifted its own backstory – more than a McGuffin, it was originally owned by a treasure hunter, who admires the young Indy’s chutzpah and passes on his hat.

With Dr Jones’ views on ancient relics in mind, it is fitting that the hat worn by Ford in The Last Crusade is now held by the Smithsonian, although in a storage unit perhaps like the Ark of the Covenant rather than on display. Fans, though, can reclaim their own piece of history with a replica. In the decade after Raider’s release, various manufacturers including Stetson held licences to produce official Indiana Jones merchandise. But the grail you’re searching for is Herbert Johnson’s original Poet model, still handcrafted to this day, but with the addition of a “Raider’s Turn”, the slight kink in the brim that made Indy’s hat his own.