Cinema audiences were introduced to the terrifying Darth Vader when he appeared through the smoky residue of a laser battle at the beginning of Star Wars (1977). First came the silhouette of his swishing cape and flared helmet, then in closeup the chilling details of his mask – the blank, fly-like eyes, the grille redolent of a mouth with gritted teeth.

Ralph McQuarrie drew the original sketches of the character and the costume designer John Mollo made them a frightening reality, but it was the British actor and former weightlifter David Prowse who was inside the suit and behind the mask. Prowse, who has died aged 85, was the one responsible for Vader’s imposing physicality and distinctive sweeping movements, curiously graceful for one so large (the actor stood 6ft 7in and weighed 19st at the time).

It was one of the peculiarities of his particular species of fame that while he played arguably the most memorable character in one of the biggest movies of all time, he could still walk down most streets without fear of being recognised.

Even his voice would not have given him away: though he spoke Vader’s lines during filming, and was assured by the writer-director George Lucas that he would be required later for the dubbing sessions, it was the American actor James Earl Jones who delivered the character’s dialogue in the finished film. It was decided that Prowse’s thick West Country burr, which earned him the nickname “Darth Farmer” from other cast members, would not have struck quite the right note of menace for an intergalactic villain.

Nor did he get to supply Vader’s menacing heavy breathing (that was the sound designer Ben Burtt, using scuba-diving apparatus). And though he performed his share of the light-sabre duels in the first picture, they were mostly handed over to the stunt department for the sequels The Empire Strikes Back (1980) and Return of the Jedi (1983). When Vader was unmasked in the latter film, moments before his death, it was the actor Sebastian Shaw, rather than Prowse, whose face was shown, and who got to speak the character’s final words. To add insult to anonymity, this death scene was concealed from Prowse, who claimed not to have been shown script pages during shooting.

Such slights were in keeping with his general frustrations about the role. “As Darth Vader, you always feel as if fame and fortune’s coming towards you, but, just as it’s going to hit, it passes you by,” he lamented. “Sometimes in the cinema, I want to yell out: ‘Hey, that’s me up there, that’s me you’re all watching.’”

Prowse was born in Bristol and was raised by his mother after his father died when he was five. He was educated at Bristol grammar school and from the age of 12 spent three years wearing a leg-iron because of suspected tuberculosis of the knee, a diagnosis that later proved to be unfounded.

At 16 he dedicated himself to bodybuilding and at the age of 25, having worked as a lifeguard and a bouncer, he entered the Mr Universe contest, during which a judge told him he would never win because of his “ugly feet”. He switched to competitive weightlifting and went on to be British heavyweight champion for three consecutive years from 1962.

While selling equipment in a gym in the early 1960s, he was approached by an acting agent who invited him to play the part of Death in Don’t Let Summer Come at the Mermaid theatre in London. From there, he moved on to commercials, television series and eventually films. He made an uncredited appearance in the star-studded James Bond comedy Casino Royale (1967), as Frankenstein’s monster, later reprising the role in a more orthodox context in The Horror of Frankenstein (1970) and Frankenstein and the Monster from Hell (1974).

He opened his first gymnasium in south London in 1969; his clients included Arnold Schwarzenegger and the Conservative prime minister Edward Heath. He also became a fitness consultant at Harrod’s while keeping his hand in with acting. His most notable pre-Star Wars credit was Stanley Kubrick’s A Clockwork Orange, in which he was the bodyguard to the writer played by Patrick Magee.

He starred in comedies including Carry On Henry (also 1971) and Terry Gilliam’s Jabberwocky (1977), and appeared with his future Star Wars co-star Carrie Fisher in her mother Debbie Reynolds’s show at the London Palladium in 1974.

Shortly before Lucas’s movie started shooting in 1976, Prowse began his 14-year stint as the superhero-like Green Cross Man in a popular series of road safety commercials. His voice was dubbed by another actor for the first two advertisements, but reinstated thereafter. The Sunday Times reported in 1978 that the first two years of Prowse’s tenure helped bring about a 5% reduction in road safety accidents in the 4-11 age group. As part of his contract with the Department of Transport, he toured schools as the Green Cross Man.

After playing Vader, Prowse’s acting roles were few and far between. He was turned down for the lead in Superman The Movie (1978), but gave the successful candidate, Christopher Reeve, physical training “I spent six weeks trying to make him look like me,” Prowse said. He performed the same function for Cary Elwes in preparation for The Princess Bride (1987).

A hip injury in 1989, as well as arthritis and various health issues relating to his ankle and spine, put Prowse out of action. In 2000, he contracted a blood disease that caused temporary paralysis in his arms. Still he lobbied at every opportunity to be considered for any future Star Wars films, and continued to mourn what he regarded as his slapdash treatment on the earlier instalments.

By 2005, he told Empire magazine that he was doing “nothing else” except being paid to fly all over the world attending Star Wars conventions, which made it all the more galling for him when in 2010 he alleged that he had been banned from any future events. “People ask what went wrong with George Lucas but to be honest, I still don’t really know,” he said. “The only thing I’ve been told is I’ve burned too many bridges between Lucasfilm and myself.”

One theory is that the director suspected Prowse of leaking in advance of the release of The Empire Strikes Back the revelation that Vader was the father of the film’s hero, Luke Skywalker.

Though never formerly politically outspoken, Prowse publicly declared his support in 2009 for Ukip, the UK Independence party. Asked in 2014 what he would do if he ruled the galaxy, he said he would “reintroduce capital punishment”. He briefly managed the Welsh musician Jayce Lewis and wrote an autobiography, Straight from the Force’s Mouth (2016), as well as recording an audiobook version that ran for 540 minutes.

In 1963 he married Norma Scammell. She survives him, along with their three children, Steve, James and Rachel.

• David Prowse, weightlifter and actor, born 1 July 1935; died 28 November 2020