It’s almost as if Jean-Paul Sartre himself appeared on screen toting a .44 Magnum (“There is no reality except in action, punk!”). The existential hero is making a comeback in mainstream cinema, with Sean Penn’s ex-US special forces soldier in The Gunman the latest of several new incarnations.

Existentialism has had a rough ride ever since Sartre first declared “man is condemned to be free” in Being and Nothingness, in 1943. Criticised by Christians, mocked by Marxists and pushed around by postmodernists, poor existentialism is by now probably wondering what the point of its existence is.

Some of the blame for this fall from grace must be laid at the gumshoe-clad feet of film noir. Those crime films of the 1940s and 50s, with their ink-black shadows and hard-boiled heroes, depicted the moral ambiguity of existentialism – the “absurdity” of life – so stylishly that their generic tropes are etched on the psyche of cinemagoers, becoming ripe for ridicule and pastiche.

Film noir may also have unwittingly contributed to existentialism’s undeserved reputation for nihilism. (Think of Robert Mitchum’s comment on gambling – and perhaps life in general – in Out of the Past: “There’s a way to lose more slowly.”) Sartre’s ideas were, in fact, essentially optimistic. Acknowledging that man is, in Heidegger’s words, “cast into the world merely to die there” is only the beginning. Existentialism is primarily concerned with transcending the futility of life through honesty and bravery. It advocates freedom, individuality and responsibility.

Recently, however, cinematic explorations of existentialism appear to be in resurgence. As well as Penn’s Jim Terrier in The Gunman, Dying of the Light by Paul Schrader and Blackhat by Michael Mann also feature contemporary manifestations of the existential hero of yore. The Double and Enemy deal with Sartrian concepts of identity and “bad faith”, the doppelganger in both films providing a perfect metaphor for the psychic split caused by pressure from an external value system. These protagonists are compelled to create a new self based on these values, and we then follow their journey towards “authenticity”, a renewed faith in internal values and self-belief. David Cronenberg, a self-described “card-carrying existentialist”, has explored similar themes in A History of Violence, Eastern Promises, and Maps to the Stars.

Of today’s existentially minded film-makers, Mann cleaves most closely to the noir template. The trench coats might be Armani and the shadows blue tinted, but Mann’s cities are firmly situated in noir country: paranoid, morally ambiguous, populated by almost interchangeable cops and criminals. Mann’s heroes, from Frank in his 1981 film Thief to Nick Hathaway in this year’s Blackhat, follow a self-created, samurai-like moral code. Adherence to theis code is a matter of survival – sometimes literal but always spiritual, their precepts are carved into the stone of their hearts.

To imbue such implacable characters with humanity takes actors of a particular calibre, which explains why Blackhat may not quite measure up to Mann’s earlier Heat or Manhunter. In the former, Robert De Niro and Al Pacino express the damage caused both to themselves and those around them by the existential obsession – the bad faith – of their characters. Without the honesty of such performances, the film would be left only with stylish but empty generic cyphers.

For Schrader, the existential hero’s on-screen lineage can be traced back to European cinema and the beautifully austere films of Carl Dreyer and Robert Bresson – in particular the latter’s Diary of a Country Priest (1956) and Pickpocket (1959). Schrader has described Taxi Driver (for which he wrote the screenplay), American Gigolo, and Light Sleeper as a trilogy featuring the same protagonist at different stages of his life. Dying of the Light was originally supposed to depict Schrader’s existential hero – here played by Nicolas Cage, as ex-CIA operative Evan Lake – in middle age, suffering from early onset dementia. However, after a studio re-edit and rescoring what we actually get is scene after disjointed scene of Cage apparently channelling Victor Meldrew, all but stamping his foot and shouting “I DON’T BELIEEEEVE IT!” in the face of his imminent existential demise.

In The Gunman a medical condition also provides the metaphor, sledgehammer style, for existential crisis. Piercing headaches prompt Penn’s character to undergo a brain scan that reveals a latent post-concussive disorder; symptoms include depression and suicidal thoughts. Any stress is likely to tip him over the edge – unfortunate in an action movie that doesn’t skimp on explosive gunshots and high-octane drama. The Gunman fulfils all the requirements of genre, while remaining firmly based on fact. It has a rawness, something of a Sam Fuller quality, as if the story has been ripped from the headlines, the plot points spat through gritted, cigar-clenching teeth.

Penn has commented that “calling [The Gunman] an ‘action film’ is kind of like calling Meryl Streep a sexy blonde chick. She is. But that really doesn’t tell the story of what she is at all.” The actor shares a screenplay credit on the film, and his career-long preoccupation with existential exploration, in his choice of acting roles and in his writing and directing – The Indian Runner, The Crossing Guard, The Pledge – is very present here. There is the act of “bad faith”: the assassination Terrier commits early in the film at the behest of a shadowy group involved in the exploitation of African mineral resources, and the journey through guilt and regret towards the redemption of existential “authenticity”.

The Gunman also appears to be an experiment for Penn, an attempt to express his political and humanist concerns within the most basic generic form. The weight of these ideas, combined with such a formidable cast (including Ray Winstone, Javier Bardem, and Mark Rylance growling his way through the duplicitous Brit role), is perhaps too much for the structure to hold. Despite this, of all the recent mainstream films in which we might discern spiritual and philosophical themes, The Gunman delivers an existentialist message of compassion and moral responsibility with the most clarity.