As an extraordinarily close confidant of President Lyndon Johnson, Jack Valenti idolised LBJ to the point of sycophancy. But he came into his own as Hollywood’s chief lobbyist in Washington. A wily defender of the big studios for almost 40 years, he swept away the old morality code of the 1930s.

When Valenti took over at the Motion Picture Association of America in 1966, the Hays Code banned not only nudity but interracial relationships and open-mouthed kissing. A couple in bed each had to have one foot on the floor.

Valenti quickly realised that change was necessary, and the issue came to a head in the rather absurd haggling over exactly how much profanity could be allowed in powerful films such as Who’s Afraid of Virginia Woolf? and Antonioni’s Blowup. “I knew I had to move swiftly and I did,” he recalled. By late 1968 he had persuaded cinemas and studios to agree to a voluntary code, to stave off government regulation. The system was based on ratings of G (for general admission) M (later PG), R and X. It is essentially unchanged to this day, although an intermediate PG-13 was added in 1984.

Valenti was often attacked for his defence of cinematic sex and violence, and his classification system was accused of secrecy and conservatism. But such criticism perhaps misses the point. Valenti had no desire to be a moral guardian to America. “I believe that every director has the right to make the movies they want to make,” he said. “Everybody else has a right not to watch it.” Valenti’s job was to protect the interests of the film industry, and he did it supremely well. He persuaded prickly studio bosses to work together while using a combination of celebrity dazzle and political manoeuvring to win over the politicians. Steven Spielberg called him “the greatest ambassador Hollywood has ever known”.

His most impressive achievement from the point of view of his employers was the preservation of a set of arcane regulations which granted the studios sole rights over the hugely lucrative syndication of television repeats. The TV networks lobbied hard for these rules to be scrapped, and the Reagan Administration, in its zeal for deregulation, seemed certain to agree until Valenti stepped in. He deployed the Universal boss Lew Wasserman, who had once been Reagan’s agent, to persuade the President to change his mind.

Valenti could sometimes seem shortsighted in his rush to defend the vested interests of the studios. He led a vigorous campaign in the 1980s against home video, notoriously telling a congressional hearing that “the videocassette recorder is to the American film producer and the American public as the Boston Strangler is to the American woman at home alone”. Today home rental accounts for nearly half the earnings of the main studios. He retired reluctantly in 2004.

Jack Joseph Valenti was born into a Sicilian immigrant family in Houston in 1921. After leaving school at 15, he worked for a chain of cinemas, then at the Humble Oil Company, during which time he took night classes at the University of Houston.

During the Second World War he flew 51 bombing missions over Italy and was awarded the Distinguished Flying Cross. He received an MBA from Harvard in 1948, before returning to work in Humble’s advertising department.

In 1952 he co-founded his own advertising agency, which handled campaign work for Texas Democrats. This led to a meeting with Lyndon Johnson, then Senate majority leader. Valenti was mesmerised. He drooled in the Houston Post that the Senator was “unbending as a mountain crag, tough as a jungle fighter”. In 2003 he called it “an animal magnetism I never got over”.

Valenti helped with media work on the 1960 Kennedy-Johnson campaign and became even closer to Johnson when he married the Vice-President’s secretary, Mary Margaret Willey, in 1962. Johnson gave the bride away.

The following year, as Valenti put it, “an act of inscrutable fate changed my life”. He was handling the press for President Kennedy’s visit to Dallas on November 22, 1963, and was six cars behind the President when Kennedy was assassinated. In the ensuing panic, Valenti accompanied Johnson back to Washington after the new President had been sworn in aboard Air Force One. Valenti was instantly appointed a special assistant.

From then on he rarely left Johnson’s side, acting as trouble-shooter, adviser and confidant. “He gets up with me every morning. He stays with me until I go to bed,” Johnson said. “He is the only one who can really take it.”

Valenti’s admiration for Johnson was total. This brought him much mockery, and stories circulated of Johnson’s using Valenti’s lap as a footrest. He never lived down his remark in 1965: “I sleep each night a little better, a little more confidently, because Lyndon Johnson is my President.”

But it was his closeness to Johnson that made him attractive to Wasserman as a potential MPAA president. Valenti found it hard to turn down a job that would increase his salary sixfold. But he left only after an initially reluctant Johnson gave him his blessing.

In his 38 years in the job, Valenti came to relish his measure of celebrity and his regular appearances at the Academy Awards. A silver-haired, perma-tanned 5ft 7in, Valenti had a taste for tailored suits teamed with cowboy boots. He cultivated an overelaborate speaking style, ostentatiously influenced by his reading of Macaulay, Gibbon and Churchill, termed “a kind of Texas baroque” by one critic.

“I spent my entire public working career in two of life’s classic fascinations, politics and Hollywood,” he said at his retirement. “You can’t beat that.”

He is survived by his wife and three children.

Jack Valenti, president of the Motion Picture Association of America, 1966-2004, was born on September 5, 1921. He died on April 26, 2007, aged 85