The Irishman feels like a send-off. Directed by 76-year-old Martin Scorsese and starring Robert De Niro (76), Al Pacino (79) and Joe Pesci (76), three men circling a shared drain of American mob and political life on their way to the grave, The Irishman is a three-and-a-half-hour, $159 million-crime epic made at a time when the only other films permitted such budgets must feature one or more of the Chrises doing battle with anonymous pixelated foe. This film appears a last hurrah, not just for generously budgeted cinema made exclusively for grown-ups, but for a group of Hollywood veterans who are unlikely to find a platform of this magnitude again. And like any good send-off, the gang’s all here for the goodbye.

The Irishman is a picture of reunions - of old GOATs De Niro and Pacino; of ultimate actor-director team De Niro and Scorsese following a 24-year break; of Joe Pesci and anyone, after the unlikely star began a near-total retirement some two decades ago. Still, though The Irishman has received considerable attention for these re-couplings, there’s been less fanfare over the return to the Scorsese fold of the filmmaker’s oldest on-screen collaborator and original troubled young man. Despite his top billing, as crime boss Angelo Bruno, Harvey Keitel is only a cog in The Irishman’s ensemble machine. But the actor, now 80, is undeniable in his handful of scenes, so calmly commanding and grave he seems to have his own gravitational pull. Lent maximum authority by Scorsese’s camera, Keitel is as monolithic a presence in The Irishman as the film’s central trio, even if the actor doesn’t quite have the popular reputation to match.

Today, Harvey Keitel is perhaps most familiar, at least to British audiences, as pencil-moustached fixer Winston Wolfe – not the character from Pulp Fiction, but the fictional frontman of ads for insurance company Direct Line since 2014. Despite a career that stretches back half a century, unlike Robert De Niro and his bagels or Orson Welles and his frozen peas, Keitel lacks the cultural cache to sell a product in his own name. This in spite of the fact that, before DiCaprio, before even De Niro, Keitel was Martin Scorsese’s go-to actor.

Once Scorsese’s proxy, Harvey Keitel played lightly autobiographical interpretations of the filmmaker in Who’s That Knocking At My Door? and Mean Streets, before later becoming a reliably scene-stealing character actor for the director, starring as an abusive boyfriend in Alice Doesn’t Live Here Anymore and an unctuous pimp in Taxi Driver. Keitel and Scorsese made their careers together: the actor appeared in four of the director’s first five movies, beginning 52 years ago with Who’s That Knocking, both men’s feature debut. Then, after he replaced original lead Jon Voight in the role of the conflicted Charlie, Keitel loudly announced himself along with Scorsese – and De Niro – in Mean Streets.

Harvey Keitel wasn’t the all-purposes chameleon that De Niro would become for Scorsese, but he was somehow rawer, seemingly more reliant on instinct and his unpredictable magnetism in contrast to De Niro’s incredibly studied, infinitesimal brand of acting. After breaking out with Scorsese, leads followed for Keitel in acclaimed debuts from other young filmmakers including Ridley Scott (The Duellists) and Paul Schrader (Blue Collar). Still, Keitel never capitalised on the early goodwill the way Scorsese did. Into the 1980s, Scorsese continued to welcome critical and commercial appreciation. Meanwhile a glance at Keitel’s resume in the 1970s reveals an actor maybe on the cusp of stardom, with a 1980s that at first seems inexplicably obscure: a further Scorsese collaboration in 1988’s The Last Temptation of Christ aside, this was a lost decade for Keitel, explained only by the film that’s missing from his filmography.

Apocalypse Now might have made Harvey Keitel a name star; instead it cast him into relative anonymity for years. Originally cast as Captain Willard, Keitel, himself a former Marine, shot on Francis Ford Coppola’s colossal Vietnam War film for three weeks before the director decided he wasn’t “introspective” enough to play the passive Willard. And so, Martin Sheen was drafted in as Keitel’s replacement, the film found enormous success and a reputation for being artistically difficult dogged Keitel until his revival in the early ’90s.

When the career-resuscitating trio of Bugsy, Thelma & Louise and Reservoir Dogs came around, by which time he was already into his 50s, the chance to be a Hollywood leading man had passed Keitel by – although in retrospect, it seems that that role was probably never for him. Keitel has had dalliances through his career with more frivolous fare – the Tarantino-penned From Dusk Till Dawn in 1996, two National Treasure movies in the aughts – but the actor’s choice of project has been suited for wider consumption only rarely.

Keitel's characters, similarly, are not often easy to stomach. Men like The Duellists' belligerent, unfeeling Feraud have been simply difficult to warm to, but more often than not Keitel's characters are just agonisingly, at-times unpleasantly, human. For an actor so closely associated with cool tough-guy cinema, Harvey Keitel has paradoxically built his career on playing the secretly sensitive, and the emotionally wrought. The urbane, sociopathically composed Mr Wolf is an exception; the quintessential Keitel character is rather a contradiction of thuggery and soul. The epitome might be Mean Streets' Charlie, a low-level mafioso who dreams of redemption through the church, or The Piano’s George Baines, a brutish woodsman pining for romance with Holly Hunter's mute pianist. Even in Quentin Tarantino’s nihilistic noir debut, Reservoir Dogs, Keitel brings a surprising maternal quality to his homicidal bank robber caring for a dying associate following a burglary gone bad.

When Mr White weeps in the closing moments of Dogs upon discovering his friend’s betrayal, Keitel is uncomfortably vulnerable, his howling so anguished it seems almost indecent to watch. Most actors want our eyeballs, but in his most memorable moments – tenderly slow-dancing with an underage prostitute as Taxi Driver’s Sport; experiencing multiple narcotics-fuelled meltdowns as the Bad Lieutenant – Harvey Keitel challenges us to look away. At the extreme, playing Lieutenant’s despicable New York cop or a sexually intimidating gangster in Fingers, Keitel is so exposed and venal as to seem like a festering wound, though even in such cases the actor can still elicit a horrible sympathy.

Keitel has rarely played out-and-out villains, but then hardly any of his protagonists could be described as heroes, either. At his best, Keitel has spent his career attempting to locate humanity in characters who are seemingly irredeemable, and he’s done it while steadfastly refusing to make them palatable for a general audience. For a time, full-frontal nudity was a signature move for Keitel, the actor taking his proclivity to bare all to its natural conclusion through a number of his movies. Keitel has also just always been a most deadly serious actor. Despite his reputation for humourlessness, even De Niro has delivered some blackly comic masterclasses for Scorsese (he’s funny again in The Irishman). Keitel, on the other hand, has never allowed a character of his any light relief, while his preferred subject matter – Keitel, the son of Jewish immigrants, in one of his more memorable supporting roles played a Nazi officer with the run of an extermination camp in The Grey Zone – is often strictly R-rated.

Harvey Keitel, not passive enough for Apocalypse Now, was perhaps always destined for a bracket of cinema that could accommodate his insistence on being confrontational. At 80, Keitel is the oldest member of The Irishman’s principal cast, but even now the actor can induce gasps. His newest film, the WWII drama The Painted Bird, proved so controversial on the festival circuit it caused horrified walkouts, while as recently as in 2015’s Youth, Keitel was still showing a willingness to de-robe down to a bare, sagging frame for the sake of his art.

Where Scorsese, whose film tastes are wide-ranging, has always adapted in a constantly changing cinematic world, a stubborn refusal to mellow took Keitel from the heart of edgy New Hollywood in the ’70s to the fringes of modern American cinema. Though in their own ways, both Scorsese and Keitel have never stopped telling the same stories. Having together explored the underworld and interrogated damaged, self-destructive men in their beginning, director and actor have apart returned to those themes repeatedly in the years since. They return to them again with The Irishman. The film is a victory lap for its principal players, here in the twilight of their careers, but for Scorsese and Keitel, in collaboration again after a 31-year hiatus, it’s the closing of a loop.

The Irishman is in cinemas now