Established in 1968, the film rating system provides parents with the information needed to determine if a film is appropriate for their children.
The movie Starlet released in 1969 seems to be the first to use the XXX rating. It’s the story of an actress who sleeps her way to the top.
In 1969, the movie 'Starlet' was given an X rating by the MPAA for nudity and profanity, and the producers of the movie rejected it. They didn't agree with the rating and instead put in their own XXX saying, “So adult one X isn’t enough!”
Truth is, there is no such thing as a "XXX" rating. It's simply a marketing tool.
In 1968 the MPAA started rating films X if they had nudity and profanity. Today the worst a movie could get is NC-17, which means that no-one 17 or under admitted.
NC-17 is worse than R, which stands for restricted. R means a movie contains some adult material and parents are urged to learn more about the film before taking their young children with them.
It was in 1990 that the NC_17 rating replaced the X rating. It was also that same year that rating descriptors are added to movies, providing parents with more information about the elements of the movie.