The story of the man behind the master, Filmworker is a documentary portrait of Leon Vitali. A one-time actor, for almost a quarter of a century Vitali was the personal assistant to legendary filmmaker Stanley Kubrick. They met on Kubrick's 1975 Thackeray adaptation Barry Lyndon, when Vitali was cast as Lord Bullingdon. The experience was wondrous, but Vitali was able to deepen his relationship with the director when Kubrick asked if he would travel to America to audition children for his next film, his take on Stephen King's The Shining.

From that moment, Vitali was in full-time employment, the conduit between Kubrick and the world until the filmmaker's death in 1999, shortly after completion of his final film, Eyes Wide Shut. In between, there was just 1987's Vietnam drama Full Metal Jacket. But Vitali's work was non-stop, dealing with the perfectionist director who kept abreast of everything connected to his films, from posters to prints. It required the patience of a saint; Kubrick was frequently foul-tempered and always obsessive.

Filmworker's own director Tony Zierra doesn't attempt anything flash; the ageing Vitali is interviewed several times, in various locations. Other interviewees include Danny Lloyd – the boy that Vitali found for The Shining – and Barry Lyndon's lead Ryan O'Neal. Full Metal Jacket's Matthew Modine and, poignantly, R Lee Ermey, who died recently, are also included, alongside Vitali's grown-up children who, you sense, lost their father to Kubrick during their upbringing.

The title refers to the occupation Vitali puts on his passport and visa forms, and he comes across as down-to-earth as that suggests. He also remains a Kubrick devotee, and the final part of the film is particularly sad. After Kubrick's death, Vitali's efforts got overlooked. Thankfully, Filmworker is an assured tribute to an unsung hero who made invaluable contributions to the work of a genius director.

Limited release from Fri 18 May.