On the drawing board she was “Project 112”. Early on, they toyed with calling her Domino, but finally settled on R4, plain and simple. It was 1956 when Renault’s chairman, Pierre Dreyfus, had a hunch people were ready for a “blue jeans” kind of car. Something they could live with every day, whether packing it to the gills with work tools, loading up the week’s groceries, or taking the family for a Sunday picnic.

As the first multi-purpose car, this was a revolution. It took some back-to-front thinking to get there, though, starting with putting the motor up front. This made it possible to morph from family sedan to utility van in one flick of the fold-away seats. Even the flip-up boot door was a world first, copied by every carmaker since. Talk about “driving the change”!

The second revolution was the price. Dreyfus wanted to make this the French car anyone could afford, so he told his designers it should cost the customer “350,000 francs and not a cent more” (or roughly $50 in 1961 money). Office wags called it “Project 350”.

Pierre Dreyfus was so excited about his “baby”, he couldn’t resist turning up for the secret road tests in Sardinia. Like a pesky schoolboy, he asked the test driver if he could take her for a spin. Unfortunately, Dreyfus lost control on a treacherous road, sending them both crashing into a ravine kamikaze-style.

So what happens when the boss crashes the prototype? You say nothing. The hapless test-driver-turned-passenger, Louis Buty, was injured, but to protect the secrecy of the tests, and keep spying competitors off the scent, they invented a story about a car accident. Of course there were rumours. Something to do with a girl… Once the car was an established success, Dreyfus came clean with the real story.

Although none of the original design team is left to tell the tale, we do know that practical features were more important than show-off looks. For the car’s Italian launch in 1961, a famous gorgeous model refused to be photographed with the Renault 4 because she didn’t find it glamorous enough. Four young French women weren’t so fickle though, when Renault sent them on a special mission: to drive a Renault 4 from Tierra del Fuego to Alaska. They did it and Renault still has the travel-scarred car to prove it. Along with the classic signs of wear and tear is a list of boys’ names scratched into the panelwork. Decades later, one of the “girls” admits these were young men they met along the way. It was the Swinging 60s, after all!

Clearly, it’s what’s inside that counts. Because our heroine went on to win the hearts of countless admirers, selling more than 8 million in 100 countries around the world. Today, collectors go wild over a rare model of Renault 4, especially if it’s an early one. Jean-François Préveraud considers himself the luckiest Renault 4 collector on earth. He owns a car with plaque number 191, the earliest known example. As he says: “She’s spotted with rust, undriveable and really doesn’t look great. But she’s the most beautiful piece in my collection.”

It’s not every day you’re 50 years young, so the Renault 4 is being treated to all the primping and preening you’d expect for such classic curves. One man behind the scenes is Raul Vazquez, whose CV includes assembling R4s in the 1970s at Renault’s Ile Seguin factory in the Paris suburbs.

Taking his hard-earned retirement in December 2010, he spent the last 18 years lavishing attentions on Renault’s own vehicle collection. His final labour of love was helping prepare many of the show-stopper Renault 4s for their 50th birthday bash. “The younger mechanics know I worked on the original assembly line, so they’re always asking ‘how does this piece go on’ or ‘where does this go’. I find it very touching.”

Coming soon: the Renault 4 goes racing…

• Biggest selling French car worldwide ever
• 3rd top selling car in history
• 8,135,424 sold
• 33 years of production, 1961-94 (ending in Morocco and Slovenia)