Hollywood loves its book adaptations—and for good reason: a staggering eighteen of the twenty films with the all-time biggest opening weekends were based on books or comic books.

If you’re wondering, the remaining two were inspired by a theme park ride. (Hint: it has to do with pirates.)

Such is the reason we’ve grown used to seeing “based on the novel by ______” or “Stephen King’s ______” adorning movie posters. However, producers aren’t always so quick to publicize their source material. Here are five well-known films with little-known pasts on bookshelves:

 

Die Hard (1988)

One of the most important action films of the eighties, Die Hard is adapted from Roderick Thorp’s 1979 novel Nothing Lasts Forever. Bringing significant changes from the book, it could have easily been a very different film.

For starters, it was originally adapted with an eye for Frank Sinatra to play the lead as a World War II veteran and retired New York City police officer. The producers essentially cut the hero’s age in half by casting Bruce Willis. Conversely, they doubled the age of the hero’s captive family member—as he’s visiting his daughter in the book, not his wife.

In addition, the terrorists in the book actually are terrorists, not just thieves. They’re not motivated by money, but politics. Oh, and Hans Gruber? His name in the book is Anton—and his nickname is “Little Tony.” The novel was out of print for years, but rereleased for the film’s 25th anniversary and is worth a read for die hard fans of Die Hard.

*Die Hard II: Die Harder, it happens, is based on a completely different book—Walter Wager’s 58 Minutes, but we’re counting the franchise as one.

 
Fast Times at Ridgemont High (1982)

Perhaps the only thing more outlandishly 80s than Fast Times at Ridgemont High is the fact that its writer, Cameron Crowe, spent a year posing as a high school student in order to research the story—which first appeared in book form.

In 1979, at the age of 22, Crowe moved in with his parents and enrolled in the local high school as a student. No one in the school knew his real age or name except for the principal, who agreed to his “experiment.” (We all know that would never, ever happen today.) Two years later Crowe published Fast Times at Ridgemont High: A True Story based on his embedded experiences—and a year after that the adapted movie hit theatres.

For some completely unacceptable reason, the book remains out of print—with used copies selling for more than $100 in “acceptable” condition. Still, it’s probably worth it.

 

The Princess Bride (1987)

Yes, Buttercup, Westley, and the six-fingered man were first characters in a book (of the same name) more than a decade before the film. Both the book and movie share the same general plot points as well as the unique plot device of a narrator who reads only “the good parts.”

The book is still in print. However, if you come across a version that claims to be “abridged” by William Goldman, rest assured it’s the full version. Goldman is indeed the author of The Princess Bride. However, like the film, the novel presents a tale-within-a-tale by voicing the narrator’s reflection on a classic romance work by S. Morgenstern. In reality, there’s no classic work and no Morgenstern. In the film, this is accomplished by showing a grandfather (played by Peter Falk) reading the book to his ill grandson (played by Fred Savage), while in the book, the narrator’s audience is his son.

 

Weird Science (1985)

We take it back. With John Hughes as its director, teenagers (among them, Robert Downey Jr. and Anthony Michael Hall) wearing bras on their heads, and a theme song performed by Oingo Boingo, Weird Science might be more outlandishly 80s than Fast Times, if not the story behind it.

Interestingly enough, all of the above came out of a 1951 comic book of the same name. Specifically, the film is an adaptation of issue five, titled “Made of the Future!” In the original story, it’s not hormonal teenagers that set out to create a woman using a computer, but a time traveler in search of a wife. The original comic sold for ten cents, but copies can now sell for more than $100 depending on their condition.

 

Mrs. Doubtfire (1993)

Moving firmly into the nineties (with no less than House of Pain’s “Jump Around” on its soundtrack), the classic dad-turned-nanny flick Mrs. Doubtfire was adapted from Anne Fine’s Madame Doubtfire. It was published in Britain in 1987 and given the title Alias Madame Doubtfire here in the United States.

In the book, the older children recognize their father from the start—whereas his makeup fools them in the movie—but that’s the only glaring difference. Other than, of course, a brilliant performance from Robin Williams.

RIP Mr. Williams. Thanks for your decades of entertainment.