The superhero soap opera

Yet all these and more very adult themes were at the core of The Avengers, the superhero comic which changed the genre forever and sprawled over five decades of sexual revolution, global upheaval, the threatened implosion of the company which published it, and the rise of the superhero blockbuster to become the dominant cinema genre.

The Avengers veered from alien soap to existential essay to Boy's Own adventure in a manner which remains astonishing today, and is in a different universe to the long-awaited and much-hyped big-screen debut, Avengers Assemble, due to hit (and no doubt save) the world next week.

It was a simple idea: throw together a bunch of established and popular comic-book heroes – Thor, the Incredible Hulk, Iron Man, Ant/Giant Man, Wasp and, from issue 2, Captain America, and – wham (!) – you capture the attention of five groups of fans and sit back to watch the sales records smash (!). It wasn't even a new idea. Creators Marvel had been beaten to the punch (! ... oh, forget it) by arch-enemy DC with the Justice League of America in 1960 (Superman, Batman, Wonder Woman, Flash, Green Lantern, Aquaman and the Martian Manhunter, since you ask).

But The Avengers developed in ways which even its creators could hardly have envisaged to encompass a massive and bewildering array of costumed, damaged beings who randomly came and went, changed costumes and sides, lost their powers and gained new ones, and spun into sub-plots with so many twists and turns that eventually the whole thing threatened to crumble under its own weight.

Actually ... it did crumble. The whole mess became so convoluted that The Avengers had to be reimagined in an alternative universe where all the characters had completely different backstories. That storyline was penned after Marvel subcontracted out The Avengers, along with Captain America, The Fantastic Four and Iron Man, for a year. When the time was up, The Avengers somehow had to be brought back to their original world. Honestly, I'm not going to tell you any more. It would just confuse you.

But here's just one plotline to give you a feel for the general lunacy: there's this woman, who has a pretty uncontrollable power of cursing people, who escapes the bad guys with her brother, falls in love with a weird being who isn't human and so feels he can't commit but eventually finds out he might be slightly human so they get married and have kids but the kids aren't real and he goes missing and she goes nuts. With me so far? Then it turns out her power is actually unimaginably huge but because she's crazy she kills many of her fellow Avengers and the whole goddamn universe with them. I mean, all Superman had to deal with was that Kryptonite stuff.

But then there was always a gaping chasm between DC and Marvel characters. Superman and Batman had problems but they generally concerned the bad guys or the protection of their secret identities, not real, existential soul-searching. Even the romantic triangle of Superman/Clark Kent, Lois Lane and Lana Lang was mostly played for laughs. And let's not even mention the occasional (but not occasional enough) "comedy" issues of Superman, many featuring the particularly useless villain Mr Mxyzptlk, which undermined the credibility of not only Superman but the entire DC universe.

Marvel, on the other hand, always tried to make their superheroes out of flesh and blood. Spider-Man was a teenager with financial problems struggling to make sense of a family tragedy; Captain America was tortured by guilt over the death of his wartime partner; the X-Men had ambivalent feelings towards mistrustful homo sapiens.

It's hard to remember now, but in an era years before the masterful Batman reboot of Frank Miller's The Dark Knight Returns and the subversion of Watchmen and Kick-Ass, Marvel's focus on character and the darkness within its heroes was revolutionary.

The first Avenger comics contained little to suggest the mind-bending plots which were to come. Thor and Iron Man had little of the characteristics which made their own comics interesting (admittedly "interesting" is pushing it for Iron Man, possibly the only Marvel comic book character who is actually stronger, and more nuanced, on film). The Hulk was compromised by the difficulty in explaining how an irrational, amoral monster could function as a team player fighting with the forces of good. Captain America, who joined only after being revived from the block of ice which had imprisoned yet kept him alive since the Second World War, did little apart from going on and on about how the world had changed.

That left Giant-Man and Wasp, a couple whose romance was at the heart of The Avengers story, but who have inexplicably and controversially been entirely written out of the movie.

Giant-Man was Henry Pym, a scientific genius who had discovered a pill that allowed him to shrink or grow. He first appeared as Ant-Man but had adopted the larger format by the second Avengers comic, supposedly because the testosterone heroics of Iron Man and Thor made him feel inadequate (plot spoiler: this will be important later on). His girlfriend and later wife, Janet van Dyne, also used the pills but grew wings when she shrank.

Pym later became Goliath and then Yellowjacket, a predilection for changing personas which predated David Bowie but which also hinted at a mental instability which grew when he assaulted his wife. The couple divorced, Pym descended further into madness, was framed and then jailed. He reacted to the later death of his wife in the only way he knew how: by changing costume and name and re-emerging as The New Wasp.

But it is Pym's descent into human frailty and marital discord that gives The Avengers its heart and soul. The film franchise will be the worse for his loss.

Pym and The Avengers weren't the only ones having very adult problems in the latter half of the 1990s. The comic industry in general had slumped. Experiments such as the Onslaught Saga, which featured a whole host of Marvel titles and characters in an overarching, crossover narrative, had lost readers, and in December 1996 Marvel filed for bankruptcy protection.

Disaster was averted by the formation of a new corporation, Marvel Enterprises. But it was the local multiplex which was to transform Marvel fortunes, when long-awaited and tortuous plans to bring its cast of superheroes to the big screen finally bore fruit with the arrival of X-Men in 2000. Discussion of the project had begun in the early 1990s with director James Cameron, but it was The Usual Suspects director Bryan Singer who fused the comic's themes of prejudice and discrimination with the language of the blockbuster to begin the reinvention of the superhero movie as the dominant genre of early 21st-century cinema.

Since then we have seen the Spider-Man franchise (incredibly successful), the Hulk (less so), more X-Men, Iron Man, Thor, Captain America - and now, at last, The Avengers.

The most artistically successful franchise has been the reboot of Batman, surprising given the unpromising source material, the kitsch awfulness of the 1960s TV series and the descent of the Tim Burton vision of the Caped Crusader into the camp crap of 1997's Batman And Robin. Christopher Nolan's Batman Begins and The Dark Knight created a world of shadows, inhabited by compromised and defeated characters, infected by a a sense of evil about to be unleashed.

The Marvel film franchises have not yet matched that terrible darkness, and the individual Avenger films which have preceded the big one have seen diminishing returns. Iron Man 2 was less impressive than Iron Man; Thor was hampered by director Kenneth Branagh's decision to play the hero's otherworldly backstory largely for laughs; Captain America was just a little routine, not inventive enough, to overcome the inbuilt flaw: the inherent jingoism central to its hero's character.

But the box office has loved them. Iron Man was the first film of 2008 to pass the $300 million mark in US domestic ticket sales; the sequel was the third-highest-grossing film of 2010 in the US and Canada. Thor was less successful but still the 10th-highest-grossing film in North America in 2011; Captain America is listed as being the third most successful film set during the Second World War.

So the stakes are high for The Avengers. The audience's hunger for superhero action fare cannot last forever. There are still plenty of brilliant Marvel characters whose adventures have not yet made it to the big screen – the best are surely the surgeon-cum-supernatural magician Dr Strange and the ultimate anti-hero, Prince Namor, the Sub-Mariner – but the public appetite for dysfunctional depressives in strange costumes cannot grow exponentially forever.

Will Avengers Assemble be the genre's climactic triumph, or the beginning of the end?