The Kennedys on screen. Has there been a single family that’s been more re-imagined, recast and re-created in the annals of filmed entertainment? In countless TV movies, mini-series and big screen epics they appear to us as instantly recognisable figures from the pop cultural pantheon. Whether it’s Robert Kennedy and JFK taking centre stage in the Cuban missile crisis drama Thirteen Days, or JFK doing strong support in films such as Ruby, or even Edward Kennedy appearing in A Woman Named Jackie, we recognise the looks, the style and the behavioural tics of America’s first political family. They have, in many cases, become as familiar to us as Elvis Presley and Marilyn Monroe.

Enter, stage left, Bobby. A star-soaked character piece directed by the former Brat-Packing actor Emilio Estevez, the movie describes a day in the life of LA’s Ambassador hotel — the staff squabbles, the guest crises, and the controlled chaos that all lead up to the assassination of Robert F. Kennedy in the hotel’s kitchen in the early hours of June 5, 1968. The movie, a hard-fought labour of love for Estevez, features stars such as Sharon Stone, Demi Moore and Anthony Hopkins in largely fictionalised roles. The one key real-life character in the film, of course, is the title role.

In this film Robert Kennedy is glimpsed only in passing. His speeches play on the soundtrack, but he has only one line on camera. He is a presence, more symbolic than flesh-and-blood (like the character of Christ in William Wyler’s Ben-Hur). And yet the legacy of screen Kennedys is so overwhelming, and the familiarity with the legend so acute, that whoever plays “Bobby” in Bobby has to get it right.

So imagine the surprise of Bobby’s 36-year-old production designer Dave Fraunces when he was chosen, over a plethora of so-called “real actors”, to take the Kennedy challenge. After digesting hours of archive footage, Fraunces divested himself of 15 superfluous pounds of body fat, was lathered over hands and face with Bobby’s “rugged outdoorsman tan” and was fitted with a hefty frontal fringe extension to give the impression of that classic Kennedy thatch. He says that he also worked on Kennedy’s idiosyncratic mien. “He had this one unique physical tick,” he explains. “Because he didn’t hear very well he would constantly be, like, leaning down, and he would tilt his good ear to whoever he was speaking to.”

Fraunces says that the process of going from a humble production designer to a screen Kennedy was nerve-jangling. “On the second day of shooting I was standing there in front of about 150 extras, and this vast array of actors. In that situation you want to do the role justice, and you just don’t want it to be distracting for them.”

It is, of course, entirely appropriate that Fraunces be nervous in front of Martin Sheen. For the 66-year-old actor is a walking anthology of iconic celluloid Kennedys. He famously played Robert Kennedy in the landmark 1974 TV movie The Missiles of October (opposite William Devane’s JFK). He then played JFK in the seminal 1980s mini-series Kennedy, for which he received a Golden Globe nomination. He even provided the narration for Oliver Stone’s JFK .

Other notable actors to tackle Kennedys have included Estevez’s former Brat Pack buddy Andrew McCarthy (Pretty in Pink), who played Robert Kennedy in the tele-movie biopic Jackie Bouvier Kennedy Onassis (2000), and the indie stalwart Martin Donovan, who became JFK for the 2002 biopic RFK. Even Henry Fonda had a go as JFK, way back in 1966, with the NBC movie The Age of Kennedy: The Early Years. Of the recent incarnations, however, Bruce Greenwood and Steven Culp as, respectively, JFK and Robert Kennedy in Thirteen Days, are most often cited as touchstones. Fraunces especially admires Culp for playing Bobby to his own strengths as an actor, “without getting bogged down in the accent and all that stuff”.

Yet there is always a danger, with a screen commodity as culturally accessible as the Kennedys, that you drift into cliché. The ghost of The Simpsons’ Kennedy-esque Mayor Quimby hangs over every screen Kennedy. Fraunces adds, sombrely, that there was no chance of parody while working on Bobby. The serious undertow of the movie, he says, was always obvious to everyone involved in its production. “Making movies is a tremendous amount of fun,” he says. “And this film was exhilarating. But when the reality of what you’re doing sinks in it becomes a much more serious thing. In this case Bobby was a righteous, driven guy. And the movie is about the potential for good that we lost when he died.”

He suggests, too, that this is also why the Kennedys continue to fascinate us, why their legacy endures, and why we continue to see them re-created before us on our screens. It’s not just because of the glamour inherent in some rose-tinted notion of a bygone Camelot era. Nor is it a morbid obsession with a family that was as tragic as it was successful. No, the argument goes, the lure of the Kennedys, especially the lure of Bobby, is that it gives us a glimpse of a kinder, more compassionate political future that never arrived.

• Bobby is screening at The Times BFI 50th London Film Festival (www.lff.org.uk 020-7928 3232), Thur and Fri

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