It started with an Instagram post. When French online-only retailer Sézane launched its T-shirts, featuring the words “l’amant” written in the typeface Cooper Black, a very modern love affair was sparked between high-street fashion and this most goofy of typefaces. It has been a whirlwind: Topshop now sells a T-shirt that reads “Femme forever” across it in Cooper Black, Pull and Bear’s version reads “Babe with power vibes” and Whistles has one that says “Eh oui” in Cooper Black-inspired letters. It has become the most fashionable font of 2017.

Fashion’s affairs with typefaces have been many – from the Didone styles of Vogue to the sans serifs favoured by Chanel, Commes des Garçons and Fendi. But Cooper Black, described in the graphic design industry’s Eye Magazine as, “as eye-catching as a charging bull and as expressive as carnival barker”, doesn’t have the sleek lines or sophistication you might expect from a sartorial squeeze. For Sarah Hyndman, author of Why Fonts Matter, its round shapes make it “look like a typeface that someone is blowing up like bubblegum – it looks ready to pop.”

Facebook Twitter Pinterest Comic avec … Louie CK uses Cooper Black. Photograph: FX

So where did this font surface from? And why has mainstream fashion gone so gaga for it?

Paul McNeil, a typographic designer at MuirMcNeil and a senior lecturer in typography at the London College of Communication, thinks it has an “unexpected affability and liveliness … due partly to its bulbous serifs, its large, lower-case letters and its tiny, gleaming white counter forms.” It’s its buffoonishness, or rather the fact that it’s “balloony and pretty and nice!”, in the words of Louis CK, who used it on the credits for his sitcom Louie, that make it appealing.

Facebook Twitter Pinterest The Doors - L.A. Woman, 1971.

It could well be its brand of familiar charm that is helping it win fashion’s favour now. Hyndman says it reminds her of family trips to Butlin’s in the 70s and thinks its current fling with fashion is all about retro nostalgia – it is “an Instagram filter for fonts – it just says ‘1970s’ the minute you look at it”.

It was created by Chicago-based typographer, illustrator and commercial artist Oswald “Oz” Cooper in 1922. It quickly became ubiquitous in advertising. According to McNeil, its foundry declared it to be the “world’s bestselling typeface in 1927”. It was marketed by the foundry’s sales manager Richard N McArthur as “the selling type supreme … it made big advertisements out of little ones”. But in the 60s, its gregarious characters fell slightly out of favour with the ad world.

Nevertheless, it has become visual shorthand for the late 60s and early 70s because it was in that era that it was brought out of adland and into the popular culture mainstream on a wave of west coast harmonies, appearing on the cover of the Beach Boys’ Pet Sounds in 1966 before going on to be the typeface of choice on the Doors’ LA Woman in 1971 and David Bowie’s Ziggy Stardust in 1972. It was the typeface of The Garfield Show and M*A*S*H.

Facebook Twitter Pinterest Tyler the Creator’s 2011 LP, Goblin.

It was also in this era that it kicked off another meaningful relationship: with hip-hop. Breakdancing crews used iron-on transfers of the letters on their T-shirts as its round shapes, Hyndman says, peeled off less than sharp-edged fonts, and it later appeared on albums and merchandise. It popped up on Biz Markie’s hat in the 80s and, in its italicised version, on De La Soul’s Stakes Is High album. More recently, in nods to the earlier DIY days of hip-hop, it has been used by Odd Future, on Tyler the Creator solo albums and Frank Ocean’s Channel Orange.

In a way, it was never out of fashion – McNeil describes it as “something of an American street-culture classic”. So when mainstream fashion chooses to adorn T-shirts with Cooper Black (alongside the current crop, there were “woke” ones from American Apparel in 2010), it is subliminally referencing all these things – hip-hop, the 70s, sitcoms and now, Louis CK.

It is all of these cultural anchors that lead to another tenet of its popularity for McNeil: “a sense of authenticity: it has a cheery gaucheness that makes it look untutored and uncontrived.” Maybe it’s this that led easyJet to make it its gaudy orange typeface of choice, too – shhh, don’t tell fashion.

• This article was amended on 10 April 2017. An earlier version said incorrectly that a Sézane T-shirt had the slogan “la femme” in Cooper Black and suggested the Whistles “Eh oui” T-shirt was in that font. The photographs used with the article were changed in the light of this.