Fans of Richard Matheson’s marvellous 1954 novel I Am Legend, particularly those who demand absolute fidelity in their book to screen adaptations (a particularly pointless endeavour) will have long been disappointed by the treatment of their favourite novel. Hammer Film Productions wanted to do it in 1957 but were thwarted by the censors who objected to then violence in Matheson’s own screenplay. It ended up being made in Italy in 1964 by Ubaldo Ragona as The Last Man on Earth with Vincent Price in the title role. It’s a great film, but takes liberties, inevitably, with the story, though not as many as I Am Legend (2007) which cast Will Smith in the leading role.

Between them came Boris Sagal’s The Omega Man (stylised on screen as The Ωmega Man) which is no more true to the novel than the others, retaining the basic idea but taking it off in a very different direction to that envisioned by Matheson (“The Omega Man was so removed from my book that it didn’t even bother me” he would later say). Sagal’s version, adapted by John William and Joyce H. Corrington, retools the story as a curious mix of blaxploitation, action thriller (there’s a pretty good escape-by-motorcycle scene, complete with obligatory unconvincing stunt doubles), science fiction and post-Manson cult paranoia film. The result isn’t at all what you’d probably want from the book but it’s a huge amount of fun in its own right.

In 1977, two years after a war that saw the combatants unleashing biological weapons, former US Army doctor Robert Neville (Charlton Heston) is apparently the last untainted man left alive in Los Angeles, having somehow survived the fireball resulting from a helicopter crash, and injecting himself with an experimental vaccine. Now immune to the lingering effects of the weapons, he struggles to stay alive in a city overrun by mutated plague survivors who have banded together as the Family, led by former television news presenter Matthias (Anthony Zerbe) who are determined to eradicate all remaining traces of technology and kill Neville. He’s a prisoner in his fortress home, playing chess with a bust of Julius Caesar at night, sadly watching Michael Wadleigh’s Woodstock (1970) in a nearby cinema (“they sure don’t make pictures like that any more”) and hunting down members of the Family. He’s so lonely and isolated that when he sees a young black woman apparently unaffected by the plague, he dismisses her as a hallucination – but she’s real and when Neville is briefly captured by Matthias, it’s Lisa (Rosalind Cash) and Dutch (Paul Koslo) who come to his rescue. They introduce him to a small group of child survivors that they’ve been caring for and Neville realizes that he might be able to use his blood to create a serum that will pass his immunity on to others.

Much has been made in some quarters of the supposed irony of NRA poster boy and arch-Republican Charlton Heston playing a character who memorises verbatim, and seems to feel affinity with, the liberal platitudes of the hippies who appear in Woodstock though in truth, we shouldn’t have been that surprised at all. In 1970, when the film went into production, Heston was in the dying days of his time as a Democrat, supporting the Civil Rights Movement in the 1960s and even supporting the Gun Control Act of 1968. It wouldn’t be until 1972 when he would reject Democratic presidential nominee George McGovern in favour of the Republican Richard Nixon that his switch to a more conservative strain of politics would begin. So it’s hardly a surprise at all then that his Neville is – or at least appears to be – sympathetic to the drug-addled babblings of the Woodstock tribe and more than happy to share with Rosalind Cash one of the earliest inter-racial kisses seen in a mainstream Hollywood film. Indeed, given his support of the Gun Control Act only two years earlier, it’s surprising to see him so happily gunning down the Family members with such alarming gusto.

The film itself is no more political than any other product of a major Hollywood studio at the time, though it’s notable that the war that led to the release of the bio-weapon escalated from a border skirmish between the Soviet Union and China. The United States seem to have been innocent bystanders in the war, dragged into the conflict not by choice but by necessity. Neville may be world-weary and cynical but he lacks the bitter misanthropy of his Planet of the Apes (1968) character, Taylor. Perhaps the closest the film comes to making a political point is in its transformation of the book’s vampires into photophobic albinos, banding together under the leadership of the charismatic leader Matthias in an almost cult-like community, seemingly dedicated solely to killing Neville. Vampires were still popular characters in horror films at the time but with the memories of the atrocities at Cielo Drive still fresh in the mind of many Americans, the idea of young (ish) cults on the loose seem to have represented more of a threat to the American way of life than any undead monster.

There’s a Biblical streak that runs throughout the film, culminating in the famous final shot in which Neville, having created the serum and been killed by Matthias (by a spear of course) is seen slumped in a pool in a pose reminiscent of Christ on the cross. Subtle it isn’t, but it a makes a good deal of sense. Neville is blundering through a strange and dangerous new world, getting by almost more through sheer bloody-mindedness than with any real sense of Purpose. When we first meet him, he spends so much time at the cinema and pootling about in his Ford XL (terrific though these opening scenes of desolation are, look closely and you’ll see other cars occasionally wandering about in the distance) that he almost misses his opportunity to get home safely before night falls.

But as was always clear from the title of the novel onwards, this was a story, much like the Mad Max films, about the birth a new legend. In the initial Mad Max trilogy, the eponymous hero gradually transforms from burnt-out loner to become a legendary figure, the Road Warrior to the Great Northern Tribe and “the man who finded us, him that came to salvage” to the new citizens of a reborn Sydney. Here, the survivors will always be told about Neville’s sacrifice (given Heston’s later NRA affiliation, it’s ironic that he meets his end because his gun jams) and will remember him as some sort of saviour whose own blood gave humanity a hope of surviving. That messianic final pose really does make perfect sense.

The Omega Man would prove to be Heston’s penultimate bleak future science fiction film, following Planet of the Apes and Beneath the Planet of the Apes (1970) with Soylent Green (1973) still to come. He attacks the role with the same many intensity as he did the Apes films and it’s not hard to see why he was one of the screen’s biggest stars at the time. Like Taylor, Neville spends a lot of his time talking to himself but his gritted teeth earnestness and undoubted charisma somehow makes it all work. Cash is stuck with some of the characteristics of the emerging blaxploitation scene but is perfectly good a role originally earmarked for Diahann Carroll and Zerbe is fine as Matthias. None of them are the best performances any of them would ever give, nor are they the best turns you’ll find in a 70s science fiction film, but they do the job well enough to sell even the more ridiculous aspects of the story.

Die hard fans of the book are bound to be disappointed and probably have every right to be. One of the best aspects of the book was Matheson’s well thought out attempt to demystify the vampire, to provide some sort of pat least pseudo-scientific rationale. Making the antagonists albino mutants rather robs us of all of that. But on its own terms, divorced from the book that it’s notionally based on, The Omega Man is a cracking post-apocalyptic thriller in its own right, breezily directed by Sagal, nicely acted and certainly never dull. The critics didn’t much care for it, but the public helped it to a decent box office take and over the years it’s become a much loved example of a particular strain of pessimistic 70s science fiction cinema, entirely understandably, and deservedly, so.