Remember the scene? In the classic 1949 film noir The Third Man, two men rise to the top of the Riesenrad, the ferris wheel that dominates the Prater amusement park in the heart of Vienna. The villainous Harry Lime (played by Orson Welles with diabolical Hollywood charm) points out the tiny figures of anonymous people far below. How much, he asks his straight-laced friend Holly Martins (Joseph Cotten), would he have to be given to allow a few of them to die? Martins is shocked. Yet as they step off the wheel, Lime makes a cheerful argument in defence of evil.

‘You know what the fellow said,’ he drawls. ‘In Italy, for 30 years under the Borgias, they had warfare, terror, murder and bloodshed. But they produced Michelangelo, Leonardo da Vinci and the Renaissance. In Switzerland, they had brotherly love. They had 500 years of democracy and peace. And what did that produce? The cuckoo clock!’

This is the most famous piece of dialogue in a film once voted the greatest British movie ever, which this year marks the 75th anniversary of its release. The question is: who came up with it? It wasn’t Graham Greene, who wrote the script. The novelist admitted that the swaggering epigram was improvised by Welles on the spot. ‘What happened,’ Greene recalled, ‘was that during the shooting, it was found necessary for the timing to insert another sentence.’

So where did Welles get these lines? They apparently went down a storm, prompting ‘hoots’ of laughter from the crew. Then the production assistant Robert Dunbar was asked to track down, as quickly as possible, who said them first. Yet he ducked the task. ‘How the hell was I going to find out? Go to the British Museum? It would have taken me three weeks.’

Welles himself claimed that he had borrowed the idea from ‘an old Hungarian play’. Yet in the annals of Hungarian drama, no one has found a likely candidate. I asked Gerhard Strassgschwandtner, the director of the Third Man Museum in Vienna. His reply: ‘About the cuckoo clock speech there is no proof who wrote or quoted it first. Graham Greene said it is the best sentence in the movie, even though it was not he but Welles who wrote it. Many specialists visit our museum, and several say Mussolini once used a similar quote. Could be…’

Was it Mussolini, then? According to my friend Philipp Andrássy-Földeáky, the Italian dictator may well have had a personal grievance against the Swiss, since for two years he ‘wandered aimlessly around the country like a penniless tramp, not recognised for his political talent’. Mussolini might also have felt inclined to defend Italian artistry, of course, not to mention Italian depravity. The dubious attribution probably originated in the German dubbed script of the film, which, with Teutonic precision, attributes the quote to Mussolini.

Yet no one has identified a persuasive Mussolini article or speech, which fits the bill. The same, incidentally, goes for Winston Churchill, who has also at times been given credit.

No, the true identity of the epigrammatist is clear, and it was neither a pontificating tyrant nor the growling bulldog of British patriotism. It was a humble artist – or not so humble, in fact. Despite his nod to a Hungarian play, Welles in reality owed his hat-tip to the short, dandyish, self-promoting, and in many ways Wellesian painter, James Abbott McNeill Whistler.

The author D.J. Taylor told me the novelist Anthony Powell may have been the first to make the connection. In the 1990-2 volume of his journals, Powell notes that the critique of the Swiss ‘appears first, of course, in Whistler’s Ten O’Clock Lectures… which I pointed out in Punch‘. In the original 1885 talk, Whistler argues that the most moral people are often the least artistic. For all their ‘worthiness’, for example, the Swiss ‘are left with’ the ‘clock that turns the mill’, he claims, ‘and the sudden cuckoo, with difficulty restrained in its box’.

Clearly fond of his own observation, Whistler made it more than once. In 1916, the painter Theodore Wores remembered a conversation he once had with Whistler. Wores had argued that San Francisco would one day be a centre for art, owing to its circumstances of climate and scenery. ‘But environment does not lead to a production of art,’ Whistler replied hotly. ‘Consider Switzerland. There the people have everything in the form of natural advantages—mountains, valleys and blue sky. And what have they produced? The cuckoo clock.’

At this point, we should mention the inaccuracy of Welles’s dismissal of the Swiss – his Swiss-missal, if you will – which is wrong in every detail. At the time of the Borgias, the Swiss weren’t peaceful. They were one of Europe’s most feared fighting forces. Nor did they invent the cuckoo clock, if it comes to that. Bavaria was responsible for that kitsch contraption.

And what about the claim that the Swiss have made no major contributions to world culture? I put out a call on social media for great Swiss cultural figures. In no particular order, the avalanche of answers included Klee, Tinguely, Walser, Cohen, Honegger, Dürrenmatt, Della Casa, Jung, Piaget, Giacometti, Federer, Rousseau, Zwingli, Kauffman, and Le Corbusier.

There’s an old story: Oscar Wilde and James Whistler were at a party and Whistler was on dazzling form. After the painter came out with yet another in a string of zingers, Wilde sighed and murmured, ‘I wish I’d said that.’ To which Whistler shot back, ‘You will, Oscar! You will!’ In this instance, though, it wasn’t Wilde who plagiarised Whistler. It was Welles.

Yet as Charles Drazin, author of In Search of The Third Man, points out, Welles did more than plagiarise. His theft was ‘a big improvement upon the original’, turning Whistler’s slightly clunky preaching into ‘something funny and startling’. How many of the greatest achievements in art have been built upon theft? And where does the thief end and the artist begin?

Thanks to Welles, the evolved epigram becomes an example of the argument it makes. Art cares more about beauty than truth, it turns out. Factual accuracy is neither here nor there.

When I recently paid a visit to Vienna– in order to ride the Riesenrad, explore the reeking sewers, and visit other shooting locations for The Third Man – a contact from the tourist board informed me, ‘The greatest trick the Viennese ever pulled was persuading the world that Mozart was Austrian and Hitler wasn’t.’ Welles pulled many tricks over the course of his career. One of his greatest was persuading the world, even if only for a moment, that bad guys have more fun—and that he was the first person to say so.