The weekly magazine ­Charlie Hebdo was launched in 1970 amid a burst of blasphemous laughter.

The attack last Wednesday left 12 dead and four seriously injured. This is a story of a disrespectful satirical newspaper that was intelligent and well ahead of its time.

I'd have liked to have had the courage of the editorial team behind that other great French satirical magazine Hara-Kiri who, following the death through cancer in 1983 of the talented contributor Reiser, placed a funeral wreath on his coffin with the words: "On behalf of Hara-Kiri: on sale everywhere". I'd have liked to have followed the example of that happy group, who refused to be cowed by the disappearance of one their own and the spectre of the grim reaper.

But the absolute horror of the death of those 12 human beings, killed by the bullets of a terrorist group on January 7 at the offices of Charlie Hebdo, is so ­outrageous that something sticks in the throat. Nevertheless, I have to be strong enough to say, repeat and say again - on the eve of the magazine's 45th birthday - what Charlie Hebdo was about, which was to challenge conventional thinking. It also celebrated the right to make fun of everything, including the right to make fun of things one shouldn't make fun of.

Charlie Hebdo was launched following the demise of Hara-Kiri, which was closed down by the government after running a less-than-reverential account of the death of the sacred General de Gaulle. But the government went too far and even voices from the right, such as the newspaper Figaro, leapt to the defence of Charlie Hebdo and the cause of freedom of speech.

Legally speaking, Hara-Kiri was killed off, but a replacement was not long in coming in the form of Charlie Hebdo, named after Charlie Brown of the cartoon strip. The first edition hit out at the censorship in France of those days, and the magazine soon became a success.

Within a year it was selling 120,000 copies a week, five times more than its ­predecessor. Flush with money and success, the magazine's offices became a den of legendary alcohol-soaked sex orgies.

But behind the image of sozzled ­journalists partying with topless girls, there was a team of dedicated professionals who - week in, week out - bust their guts to produce truly original cartoons that no other publication had anything like, and which had an absolutely original editorial angle on the events of the week.

It is often forgotten, but it was Charlie that introduced the environment to the French political world, at a time when the word did not appear in dictionaries. This campaigning interest in the ­environment was led by Pierre Fournier, an unusual character who wore a bowler hat and bow tie and was convinced that the world would destroy itself if it continued to produce and consume so much.

Not many people believed him, not even at Charlie, but he was given the freedom to express himself in the monthly title "La Guele Ouverte" (the open gob), which ran from 1972 to 1977 as "the journal which announces the end of the world".

When, in July 1971, Charlie called for people to protest against the building of a new nuclear installation in the ­department of Ain, between 12,000 and 15,000 people showed up, leading to the creation of Europe's first popular anti-nuclear movement.

Throughout the 1970s, Charlie was well ahead of the game when it came to the central issues of the era: the environment, pacifism, anti-racism and even feminism. But, little by little, the rest of the world caught up. When ­Mitterrand and the left arrived in the Elysee Palace in 1981, the weekly paper failed to capture the spirit of the time, unlike the newspaper Liberation, the paper of the ultra- left and ultra-cool. The highly indebted Charlie relaunched itself as a daily paper, but the move did not work and the paper did not survive the money-grabbing decade of the 1980s.

The team behind the paper disbanded for almost 10 years before launching a less-than-perfect paper called La Grosse Bertha in 1990. Two years later this title was relaunched as Charlie, under the direction of Philippe Val. From the first edition of the reborn title, it was clear that the original enthusiasm and wit of the team had survived intact and it was lapped up by a public grateful for distraction and something different following the fall of the Berlin Wall and the rise of neo-liberalism.

Little by little, Val brought a more ­serious tone to the title, with learned editorial references to Spinoza and such like. But this high-mindedness began to bore some of the title's loyal readers.

During the noughties, an uneasy split in the title's editorial line began to fester. Some wanted Charlie to return to its comic roots and for it to be more ­engaging than engaged. The editorial writer ­Caroline Fourest embodied the spirit of high seriousness that her critics felt was ruining the title.

But the authoritarian Val, supported by cartoonists Cabu and Wolinski, silenced the dissidents, who had not defended themselves very strongly anyway, much to the disappointment of many readers who had hoped for a more spirited defence of the comic satirical position.

In his book Honeymoon, which appeared in 2011, one of Charlie's founders, Francois Cavanna, admitted he regretted letting Val take control of the paper, saying he had dreamed of rebuilding a truly free Charlie. But at the time, Cavanna had kept quiet like everybody else.

In July 2008, the veteran cartoonist Siné ran a sensationalised account of the conversion of president Sarkozy's son to Judaism. Val accused Siné of anti-­Semitism (of which Siné was subsequently cleared in court) and fired him, showing to the public the factions within the paper that were tearing it apart. By this stage, Charlie was no more than a shadow of its former self.

In 2009, Val left the paper to take the reins at the public radio station France Inter. He was succeeded by Stephane ­Charbonnier, known as Charb, who wanted to revive the founders' original spirit of irreverence. In doing that he rubbed up against Islam and the Prophet Mohammed.

Since the affair of the publication of cartoons of the prophet in 2006, Charlie had established through various court proceedings that it had the legal right to poke fun of religious figures as much as anyone else.

For its Charia Hebdo edition of ­November 2, 2011, the title published a cartoon of Mohammed in high spirits. Shortly afterwards, a Molotov cocktail exploded in the newspaper's offices and staff were forced to seek refuge in the offices of the newspaper Liberation and under strong police protection.

Although there were no serious ­consequences it was the first warning, which was more symbolic than anything else. On Wednesday, January 7, they tried again. And this time they succeeded.

The original French version of this ­article will be published in this ­Wednesday's edition of France's leading weekly news magazine Le Nouvel Observateur. The writer Arnaud Gonzague was a staff writer on Charlie Hebdo before moving to L'Obs, as Le Nouvel Observateur has been known since October 2014. Translation by Mark Latham