The indisputable claim to fame of “Wag” Bennett — and, it must immediately be said, of his wife Dianne, also — was the role they played in the rise to fame of Arnold Schwarzenegger, from an unknown Austrian would-be bodybuilder, desperate for a break into fame and fortune, to the Mr Universe title and thence to the US, movie stardom and the governorship of California.

It was a debt that Schwarzenegger never forgot, and he always maintained contact with the mentors whom he liked to call his “British parents”.

Schwarzenegger, born in Graz not long after the Second World War, was only 19 when he came to Britain in 1966, with his eyes on that year’s Mr Universe title. Bennett, who was one of the judges of the competition, and Dianne were impressed by the determination of the virtually penniless youth, as well as by the bizarre impression he made, almost visibly growing out of his clothes in front of them. “His trousers were flying at half mast, halfway up his calves,” Bennett recalled, so Dianne took him off to buy some boots to close the gap.”

It was to be the beginning of a nurturing relationship that was to last two years. Two of the mainstays of British bodybuilding in that era, Wag and Dianne ran two gyms in the East End, one beneath their home in Forest Gate and another farther down the Romford Road.

The Bennetts invited Schwarzenegger to share their home — no mean sacrifice, since they had six children to bring up. Bennett told the young man that he would have to sleep on the sofa, since all available beds were taken by the family, and with this arrangement working satisfactorily, they supervised his development. Bennett devised a training programme for Schwarzenegger, taught him how to pose, and chose the theme music from the film Exodus as his posing music. It was a tune Schwarzenegger was to use for years to come.

All the while Dianne cooked him his favourite meal, turkey breasts — several of which he ate every hour on the hour. And since he could not get into regulation shirts bought off the shelf, she made them for him in his favourite colours, fluorescent lime green and yellow. She also took charge of his English, which had been somewhat rudimentary on his arrival in London.

In the event, the 1966 title was to elude Schwarzenegger. He was beaten that year by the American bodybuilder Chet Yorton, whose musculature and legs were adjudged superior. Bennett immediately went to work on these areas, improving muscle definition and the power of his legs, and Schwarzenegger won his first Mr Universe title, the first of five, the following year. As Schwarzenegger was to say in paying tribute to Bennett: “The Mr Universe title was my ticket to America the land of opportunity where I could become a star and get rich.”

Charles “Wag” Bennett was born in 1930 in Canning Town, East London, where his family ran a business selling bicyles and motorbikes, and were involved in speedway. He started bodybuilding at 15 at a gym in Hackney, and by 1950 had become the first man in Britain to bench press 500lbs. He first met his future wife Dianne, herself from a bodybuilding family, when he went down to Portsmouth that year to do a show for her father, Bob Woolger.

They were married four years later and set up their first gym in Wanstead; the famous Forest Gate gym followed in 1961. Dianne posed at bodybuilding shows with her own group, Dianne Bennett’s Glamour Girls, who lifted weights to Roy Orbison’s hit song Oh, Pretty Woman. She also published a magazine, Bodypower. The pair also ran an equipment company, Everest, a supplements business called Pinnacle and edited a fitness and bodyculture magazine entitled Peak.

The Bennetts always derived a quiet satisfaction from the achievements of their prot?g?. For his part, he always kept in touch with the family and invited them to his wedding to John F. Kennedy’s niece, the television journalist Maria Shriver, at Hyannis, Massachusetts, in 1986.

Wag Bennett is survived by his wife and by five of their six children.

Charles “Wag” Bennett, bodybuilder and trainer, was born on March 29, 1930. He died of cancer on September 17, 2008, aged 78.