Carol Reed’s classic post-war mystery, The Third Man, hardly lacks for admirers. If in 1949 it was merely a well-received thriller, “a bang-up melodrama” as one New York Times reviewer put it, at some indeterminate moment it became a masterpiece – a cherished grandfather-clock in the Academy attic. In 1999, a BFI poll declared it the No. 1 greatest British film of all time. In 2018, Time Out rightly criticised this list’s lack of diversity and ran its own poll on the subject. They put The Third Man at No. 2 (after Nicholas Roeg’s Don’t Look Now). With this year’s 70-year anniversary re-release, the fanfare goes on.

Unlike other heavy-hitters in the Hall of Fame circuit – your Citizen Kane’s and your Vertigo’s – The Third Man is remarkable as an ensemble effort. Yes there’s Reed’s direction, but where would he be without Graham Greene’s screenplay? And what about Orson Welles’ “cuckoo-clock” bit? And don’t forget Alida Valli – has anyone ever been as stoically world-weary as Anna Schmidt? The whole thing’s prime real estate for theorists of authorship to duke it out and divide the territory between them.

I don’t go in for such things. But if I did, I suppose this article would plant me in the Anton Karas zone. Karas: the then-unknown Austrian musician whose Third Man zither theme has since become one of the best-loved film scores of all time.

Its jaunty opening notes accompany the title credits, which appear over a static shot of the zither’s reverberating strings. The strange instrument continues on as the film’s only source of non-diegetic music, guiding the audience with its Alpine peculiarity through all the favoured moods of a noir thriller: from suspenseful threat to out-and-out peril through to brief reprieves of tenderness, and then surely enough, back again to the tune that would make Karas famous: Harry Lime’s Theme.

Reviewers at the time jostled each other to describe the zither’s curious effect and many baroque metaphors were pressed into service (“a cloudburst of sewing needles”?). I won’t attempt my own here. But something almost everyone could agree on was the theme’s apparently ironic distance from the action.

Here was a story of shattered European dreams, of friendship betrayed and transactional murder, shot with all the murky, Expressionistic tricks in the ’40s noir handbook. And then over the top comes Harry Lime’s Theme: an ingenuous and wholly undisturbed tune, the kind that you might whistle to yourself whilst chopping vegetables. Today the contrast of dark content with chirpy music has been pumped up into a festering cliché, but in 1949 times were simpler and a film score pretty much just told you who to root for. Karas’ did not.

This was the age of the sweeping, milky orchestral arrangement. To give a solo instrument (let alone a zither – what even is it?) the full musical run of a film was a statement, and Reed knew it. Apparently after watching a preview, the chairman of British Lion – Reed’s distributer - sent him a telegram: “Dear Carol, saw The Third Man last night. Love it. I think you’ve got a big success there. But please take off the banjo”.

These doubts were misplaced.

The Third Man was released in UK cinemas on 1 September, and at that moment zither-mania was unleashed upon the world. Reed’s producers were caught with their pants down. They hurriedly pressed a record with Decca and Harry Lime’s Theme sold 500,000 copies between October and December. In the U.S., after the film’s release in February 1950, the theme spent 11 weeks at No. 1 in the Billboard charts.

Everyone wanted to know first what a zither was, and second where to buy one. Bandleaders and variety acts were quick to cater to the new craze, and there arrived a barrage of cover versions from groups with names like Guy Lombardo and His Royal Canadians and Hank “Sugarfoot” Garland and His Sugar Footers.

And at the centre of it all was the surprised Austrian zither-player, Anton Karas, who at 43 years old had become an overnight sensation. Astounded but unphased, he answered the call. From the winter of 1949 till the summer of 1950 he toured Britain and then the States. He played before a young Princess Margaret and an old Pope Pius XII, among others, and when he finally returned to Vienna in July he was welcomed home by the Austrian Chancellor and Foreign Minister like a conquering hero returning to Rome.

Karas’ rapidly ascendant celebrity came with its own pre-packaged origin story. It went that Carol Reed had discovered Karas completely by chance, busking at a kind of Austrian seasonal wine tavern called a heuriger. We can see him now, zither perched atop his lieder-hosened thighs and a rustic pipe emitting occasional blasts of smoke about his grizzled chin – totally unsuspecting. It’s a story that still persists (including on Wikipedia) even though it’s not really what happened. Karas (who was a sharp dresser often sporting a white suit, and who played his concert zither on a table-top) was actually booked to play at a welcome party for the film crew at a Viennese flat, which is where Reed first heard him. Of course, myth has more zest and flavour than pedantic fact.

On the one hand this story fulfills the fantasy of the 1930s Hollywood revue. One of the film industry’s all-time favourite fairytales about itself is that all it takes is being in the right place at the right time and bang!, you’re on a rocketship for the stars. It’s like Karas is handed Ruby Keeler’s dancing shoes and thrust suddenly into the footlights.

But it also nourishes the fictional Vienna of Reed’s film. Beyond the zither, the only music in The Third Man comes from Lime’s sinister associate, Baron Kurtz, who has a slot grinding out violin at the bordelloish Casanova Club. For Kurtz, music is a side-hustle – a little sweetener on top of however much he clears from Lime’s penicillin racket. Music is just another game in the city’s shadowy and precarious blackmarket economy.

Against this backdrop, the real gigging folk musician, the supposed heuriger busker Anton Karas brought a dose of authenticity to the venture. Reed was drawn to what he called the “gritty” quality of Karas’ playing. According to film scholar Charles Drazin, Reed was distraught when the hi-tech equipment at Shepperton Studios seemed to be recording the zither’s sound too cleanly (to counteract this, they apparently arranged for Karas to play underneath a table).

Karas’ zither is showcased with a definite edge of exoticism. Amongst the crumbling baroque apartment buildings of war-bitten Vienna, it casts an air of antique central-European inscrutability. There’s a certain xenophobia at play which Popescu, the Romanian, keenly sides with: “You’ll never teach these Austrians to be good citizens,” he tells Martins wearily.

Again, we might look to Baron Kurtz, the Austrian racketeer-violinist and Popescu’s partner in crime, played with cheeky menace by the Jewish Austrian actor, Ernst Deutsch. He famously played the villainous assistant in Paul Wegener’s silent horror, Der Golem, in 1920, and in The Third Man he reasserts his considerable talent for naughtiness. But it’s hard to shake off the feeling that Deutsch’s Semitic features are being harnessed here in a not quite appropriate way, as ethnic ambiguity converges rather too neatly with moral dissipation.

Did Karas find himself in a similar position? Was his art exploited slightly for the sake of atmospherics?

If Hollywood’s favourite fairytale is 42nd Street, its most bitter tragedy must be King Kong: the mirror-opposite of the dream come true, in which fame is rotten, obtrusive and unwelcome and only causes its beneficiary misery. This was hardly the case for Anton Karas. He had his fee, his touring money and his 50% royalties on record sales and with them he bought a heuriger in Vienna which he named Der Dritte Mann. He released some more albums, toured some, and otherwise carried on living his life.

A nice ending, without casualties, but we shouldn’t let it soothe us to sleep. The myth of Karas the star-crossed busker, and others like it, don’t actually idealise their subjects. At their core, they idealise the vast power differentials at play in film production, in which so many are vulnerable whilst a few stay invincible. And in which so few outsiders break through, which is exactly what Karas was – an outsider in the process. Surely this is what films even now so desperately need? Newcomers, strangers to the game, crooked violinists. Imagine if The Third Man’s score had been Strauss?

In a 2015 interview with The Independent, Martin Scorsese recalls what must have been a common experience in the 1950s: hearing Karas’ theme years before he actually saw the movie. “That Third Man Theme was a part of our lives,” he says. Would it be too much to say that it was Karas’ zither which guaranteed and cemented The Third Man’s reputation? Over radio airplay, on record and in bars and night-clubs, it kept images and characters alive in audience imaginations. Quick-witted musicians apparently used to start playing it whenever Orson Welles strolled into a bar for years afterwards.

Sometimes sound strikes right down into the ventricles – in a way that images just can’t. It creeps under the skin. And Anton Karas’ zither... Should I do it? Should I go in for a metaphor now?