Because of its dark nature, "Indiana Jones and the Temple of Doom" would help create PG-13 — one of the most profitable movie ratings in film history. ‘Indiana Jones And The Temple Of Doom’/LucasFilm This summer marks the 30th anniversary of the popular second installment of the Indiana Jones series, "Indiana Jones and the Temple of Doom."

However, a more important anniversary is what "Temple of Doom" helped to usher in — the creation of the PG-13 rating, a box-office sweet spot that would shape film production.

Here's how the rating came to be.

A Darker Dr. Jones

Of all the films in the Indiana Jones series, there's no doubt that 1984's PG-rated "Indiana Jones and the Temple of Doom" is the darkest.

As producer George Lucas explained to Empire, "Part of it was I was going through a divorce, Steven had just broken up, and we were not in a good mood. It ended up darker than we thought it would be. Once we got out of our bad moods ... we kind of looked at it and went, 'Mmmmm, we certainly took it to the extreme.'"

Those extremes — which included an incredibly violent human-sacrifice scene — outraged parents who brought their children to the PG-rated film. Still, the darker installment was massively popular and brought in $179 million in the U.S. alone.

"Everybody was screaming, screaming, screaming that it should have had an R-rating, and I didn’t agree," director Steven Spielberg told The Associated Press in 2004.

But with no rating in between PG and R, Spielberg would come up with a compromise that would change movies and the rating system forever.

A New Rating

"Let's call it PG-13 or PG-14," Spielberg told the head of the MPAA, Jack Valenti, about the new rating in 1984. Associated Press

Up until 1984, there had been only four ratings that a film could receive: G, PG, R, and X (which would later become NC-17).

Films like "Temple of Doom," which were too mature for PG audiences but not mature enough for the R rating, would find themselves in limbo.

Spielberg found this "netherworld" rating unfair to both filmmakers and audiences. So, according to a 2008 interview with Vanity Fair, Spielberg says he came up with a new rating that would bridge the gap:

"I remember calling Jack Valenti [then the president of the Motion Picture Association] and suggesting to him that we need a rating between R and PG, because so many films were falling into a netherworld, you know, of unfairness. Unfair that certain kids were exposed to Jaws, but also unfair that certain films were restricted, that kids who were 13, 14, 15 should be allowed to see. I suggested, 'Let’s call it PG-13 or PG-14, depending on how you want to design the slide rule,' and Jack came back to me and said, 'We’ve determined that PG-13 would be the right age for that temperature of movie.' So I’ve always been very proud that I had something to do with that rating."

On Aug. 10, 1984, only three months after parents were outraged over the release of PG-rated "Temple of Doom," "Red Dawn," a drama starring Patrick Swayze, became the first film to be released with the PG-13 rating.

The Popularity And Profitability Of PG-13

Without "Temple of Doom" we may not have one of most important movie ratings in Hollywood today. Paramount Pictures Over the next 30 years, the PG-13 rating would become one of the most popular and profitable ratings in the film industry.

Six of the top 10 highest-grossing domestic films of all time are rated PG-13.

The highest-grossing film ever, 2009's PG-13-rated "Avatar," raked in $760 million at the domestic box office, while the highest-grossing R-rated film, 2004's "The Passion of the Christ," took in a comparatively low $370 million.

With its ability to be both safe and threatening while still reaching a mass audience, the rating has become a great marketing tool for most major studios.

"In a way it’s better to get a PG-13 than a PG for certain movies," Spielberg told the AP. "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.'"