Los Angeles ? This is the story of how a gooey green guy in a microwave, a pagan witch doctor with a beating heart in his hand and that unlucky numeral 13 changed the way Hollywood made its movies.

It has been two decades since the summer of 1984, when “Gremlins” and “Indiana Jones and the Temple of Doom” caused an uproar among some parents who took their young children to the PG-rated films and walked out wishing the rating had suggested more guidance than just “parental guidance suggested.”

The solution became the PG-13 rating.

But instead of being solely an extra warning to parents, as it was originally conceived, it has evolved into the preferred rating of studios and filmmakers. As Steven Spielberg told The Associated Press recently, PG-13 puts “hot sauce” on a movie in the viewer’s mind.

The genesis of PG-13 is directly linked to Spielberg, who in 1984 became a lightning rod for parental ire.

“I created the problem, and I also supplied the solution … I invented the rating,” Spielberg, the producer of “Gremlins” and director of “Temple of Doom,” said in a recent interview.

With no middle ground between PG and R, the ratings board of the 1980s frequently wrestled with the right way to classify movies that should and should not be viewed by children. The flaw in the Motion Picture Association of America’s rating system was that it lumped all children — from infants to 17-year-olds — into the same group.

Spielberg thought it was an easy fix.

“I went to Jack Valenti (head of the MPAA), who’s a friend of mine, and I said, ‘Jack, why don’t we do a rating called PG-13, which would suit films like “Gremlins” and “Indy 2”?”‘ Spielberg said. “So I called Jack, and Jack said, ‘Leave it to me …”‘

Young visitors at Universal Studios' CityWalk stroll pass a movie marquee in the Universal City section of Los Angeles, where half of the films are rated PG-13. The rating turned 20 years old this summer.

Aug. 10, 1984, marked the first debut of a PG-13 movie: “Red Dawn,” about a communist invasion of America and the high-school rebels who fight back. PG-13 ratings that year also went to the Gene Wilder comedy “The Woman in Red,” the sci-fi epic “Dune,” Matt Dillon’s “The Flamingo Kid” and the mob farce “Johnny Dangerously.”

Studios and filmmakers did not view the new rating as a potential punishment. Rather, it was liberating, said Joe Dante, director of “Gremlins.”

Dante recalled an old B-movie saying: “An older child will NOT watch anything a younger child will watch, but a younger child will watch ANYTHING that an older child will watch.”

That philosophy transformed the PG-13 rating into a marketing tool. It promised edge without threatening offense.

“In a way it’s better to get a PG-13 than a PG for certain movies,” Spielberg said. “Sometimes PG, unless it’s for an animated movie, it turns a lot of young people off. They think it’s going to be too below their radar and they tend to want to say, ‘Well, PG-13 might have a little bit of hot sauce on it.”‘

The PG-13 rated “Titanic” is the highest-grossing movie in history, and the top 10 includes four others — both “Spider-Man” movies, “The Lord of the Rings: The Return of the King” and “Jurassic Park.”