Valenti had a stroke in March and was hospitalized for several weeks at Johns Hopkins University Medical Center in Baltimore. He left the hospital on Tuesday, according to the Hollywood Reporter.
He died of complications from the stroke at his Washington, D.C., home, said Seth Oster of the Motion Picture Association of America.
"In a sometimes unreasonable business, Jack Valenti was a giant voice of reason," Steven Spielberg said in a statement. "He was the greatest ambassador Hollywood has ever known, and I will value his wisdom and friendship for all time."
Kirk Douglas said Valenti, his friend for more than 45 years, visited him in New York City in March for a talk by the actor at a YMCA.
"Two days later, I got a call about his stroke. My wife and I flew to Johns Hopkins Hospital immediately," Douglas said. "He was in a coma. I held his hand and talked to him. Maybe he heard me. My only consolation is that he did not suffer."
Valenti was a special assistant and confidant to President Lyndon Johnson when he was lured to Hollywood in 1966 by movie moguls Lew Wasserman and Arthur Krim. A lifelong film lover, he once cited the 1966 film "A Man for All Seasons" as his all-time favorite.
When he took over as president of the Motion Picture Association of America, Valenti was caught between Hollywood's outdated system of self-censorship and the liberal cultural explosion taking place in America.
Valenti abolished the industry's restrictive Hays code, which prohibited explicit violence and frank treatment of sex, and in 1968 oversaw creation of today's letter-based ratings system.
"While I believe that every director, studio has the right to make the movies they want to make, everybody else has a right not to watch it," Valenti told The Associated Press shortly before his retirement in 2004. "All we do is give advance cautionary warnings and say this is what we think is in this movie."
Dan Glickman, his successor at the MPAA, said Thursday that Valenti embodied the "theatricality" of the industry.
"Jack was a showman, a gentleman, an orator, and a passionate champion of this country, its movies, and the enduring freedoms that made both so important to this world," Glickman said in a statement. "Jack was an original. No one will ever fill his trademark cowboy boots."
John Fithian, who heads the National Association of Theatre Owners, recalled Valenti as a wise and ready mentor. Fithian said he had lunch with Valenti shortly before his stroke.
"I was going to lunch to ask him advice actually on one or two critical issues. He was on top of his game, taking calls from leading directors in the middle of lunch to answer questions and give them advice," Fithian said.
The white-haired Valenti was familiar to movie fans through his frequent appearances at the Academy Awards, when frequent Oscar host Johnny Carson would poke fun at his speeches. But Valenti was a showman, equally animated whether testifying at a congressional hearing, hobnobbing with celebrities at the Cannes Film Festival, or previewing films for Washington's elite in his office's private theater.
His friends ranged from actors Kirk Douglas and Sidney Poitier to, more improbably, Sen. Jesse Helms, a conservative often at odds with Hollywood.
"Jack Valenti was a true leader and gentleman whose wit, fire and passion for our business inspired everyone regardless of politics or opinion, background or belief," Barry Meyer, chairman and chief executive officer of Warner Bros., said in a statement.
In Valenti's later years he handled tricky new challenges from the Internet and technologies that allow movies to be illegally reproduced and distributed in an instant. Valenti also traveled worldwide seeking to thwart movie piracy and boost film exports to reluctant countries such as China.
Valenti's Washington career was born from tragedy. As a Texas-based political consultant working for then-Vice President Johnson, Valenti was riding in the presidential motorcade on Nov. 22, 1963, when President Kennedy was assassinated in Dallas. Valenti, six cars behind the president, initially didn't know what happened.
"Without a trace of warning, the car in front of us accelerated from eight miles an hour to eighty," he wrote in his memoir, "This Time, This Place," to be published in June. "The whole spectacle turned bizarre, like an arcade game run amok, as we drove madly toward or away from some unnamed terror."
But, it was Jacqueline Kennedy's catatonic stare that was his most vivid memory of the day.
"If you look at that famous photograph, her eyes are - opaque, unseeing. I thought, 'How does this woman manage to get through..the next hour?'" he told CBS Radio in 2003.
In an Associated Press interview, he said in 2003 that the assassination "is so seared in my memory I literally, sometimes at night — not often, but once or twice a year — I relive that day."
Oliver Stone's 1991 film "JFK" angered Valenti. Stressing he wasn't speaking for the MPAA, he said the film's implication that LBJ was involved in the assassination was "quackery" plucked from a "slag heap of loony theories."
Hurried aboard Air Force One for Johnson's historic flight back to Washington, Valenti was instantly drafted as a special assistant to the new president.
On that day, Valenti remembered, Johnson "was determined to be the coolest cat on the plane, and he was. First, he wasn't leaving Dallas until the coffin of the 35th President was aboard. Second, he wanted to be sworn in on the airplane.
"I couldn't figure out why," Valenti said. "Even Bobby Kennedy was saying to him: 'Get in the air, you're president, it's ceremonial.'"
Looking back, Valenti said, he realized that Johnson wanted a picture of himself being sworn in flashed around the world before he landed at Andrews Air Force base outside Washington, to show that the nation goes on.
"He wanted Mrs. Kennedy to be in the picture," Valenti said.