Since it was published in 1971, author Jon Stone and illustrator Michael Smollin’s The Monster at the End of This Book has become an iconic entry in the kidlit canon. According to Publisher’s Weekly, Random House and Western Publishing (the company that produced Little Golden Books when The Monster at the End of This Book debuted) had reportedly sold more than 20 million copies of Stone and Smollin’s classic as of 2019.

The story is familiar to most Americans who have ever been, or met, a 5-year-old: Grover, thoroughly freaked out by the book’s title page, tries everything he can think of to keep readers from turning pages and bringing him face-to-face with the titular monster (which, spoiler alert, turns out to be him). It’s considered an influential title in the development of children’s metafiction—stories that break the fourth wall and let readers in on the act of creation. To mark its 50th anniversary, here are eight fourth-wall-smashing facts about The Monster at the End of This Book.

1. The author of The Monster at the End of This Book was one of the architects of Sesame Street.

Jon Stone got his start in television in a CBS training program shortly after earning his master’s degree from the Yale School of Drama in 1955. In 1968, after a stint as a writer for legendary kids’ variety show Captain Kangaroo, Stone was one of the original team of producers recruited by Sesame Street co-creator Joan Ganz Cooney to develop a trailblazing kids’ show that would be as educational as it was entertaining. Stone was responsible for assembling the show’s original, inclusive cast, developing some of its best-known characters, writing the pilot episode, and helping bring puppeteer Jim Henson, who created several popular Sesame Street characters, on board.

2. Sesame Street wasn’t the only way the author of The Monster at the End of This Book influenced television.

Stone helped lay the foundation for another iconic series when he collaborated with Henson on 1975’s The Muppet Show: Sex and Violence, the second of two pilots for what would eventually become The Muppet Show. Along with the first pilot—1974’s The Muppet Valentine ShowSex and Violence established several of The Muppet Show’s hallmarks, including its variety format and gently subversive humor. Sex and Violence also introduced a number of Muppet Show regulars, including Sam Eagle, Electric Mayhem frontman Dr. Teeth, and the Swedish Chef.

In a roundabout way, Stone’s influence also spilled over into the world of primetime sitcoms. Before he began his groundbreaking work on Sesame Street, Stone was the driving force behind The Munsters’s season-one casting shakeup. Beverley Owen, who played Marilyn in the first 13 episodes, left the show in 1964 to marry Stone, prompting her replacement by Pat Priest.

3. The illustrator of The Monster at the End of This Book was a decorated war veteran and prolific artist and animator.

Michael Smollin was born in 1925 to parents who immigrated to America from Eastern Europe to escape the onslaught of World War I. As an infantryman during World War II, Smollin fought in the Battle of the Bulge, where he suffered shrapnel wounds that earned him a Purple Heart and retired him from active duty. He was a prolific commercial illustrator for many years, with a client roster that included Milton Bradley, TV Guide, and Time magazine.

4. The star of The Monster at the End of This Book made his first appearance—in a radically different form—on The Ed Sullivan Show.

Audiences got their first glimpse of the Muppet who would eventually become Grover in a 1967 Christmas Eve episode of The Ed Sullivan Show. Covered with green fur and sporting an orange nose, proto-Grover (known as “Gleep”) made his debut in a sketch set in Santa’s workshop, where he was one of a crew of “thugs, crooks, and burglars” bent on disrupting Santa’s business. It wasn’t until 1970—the year before The Monster at the End of This Book was published—that Grover became a regular on Sesame Street in the form we know today: blue-furred, pink-nosed, and unfailingly agreeable.

5. The Monster at the End of This Book was written in a few hours, on a cross-country flight.

According to The Washington Post, Stone wrote the book, which clocks in at just over 350 words, on a legal pad during a flight to California sometime in late 1970 or early 1971. Stone hated flying and was likely trying to ease his anxiety … with a story about anxiety. He showed the manuscript to Christopher Cerf (son of Random House co-founder and popular game show panelist Bennett Cerf), who had spent years as a senior editor at Random House and was now tasked with developing books and other products to help fund Sesame Street. Cerf knew a thing or two about children’s literature—during his tenure at Random House, he had worked with Dr. Seuss—and he immediately knew that Stone was onto something special.

6. The Monster at the End of This Book helped generate an important revenue stream for Sesame Street.

Despite the brand’s enormous footprint in bookstores, toy stores, and even supermarkets, keeping Sesame Street on the air has always been an act of fiscal creativity. Sesame Workshop, the nonprofit that produces the show, reported an operating income of only $1.6 million in 2018, while its operating costs add up to more than $100 million per year. (The 2008 financial crisis, along with fundamental shifts in how kids play, nearly tanked the show, necessitating its controversial move to HBO.)

The Monster at the End of This Book established a key revenue stream for Sesame Street, proving that books could be an important source of income. It remains one of the 10 bestselling books in the Little Golden Books line and an important backlist title for Random House, which published the first-ever licensed Sesame Street tie-in book in 1971 and continues to release new Sesame Street-related titles every year. And Random House isn’t the show’s only licensed publishing partner; as of 2019, a combined 14 U.S. publishers were putting out about 100 new Sesame Street titles every year, thanks in large part to the breakout success of The Monster at the End of This Book.

7. The Monster at the End of This Book has influenced authors well beyond the world of children’s literature.

Brad Parks, Shamus Award-winning author of thrillers such as Say Nothing and Interference, has cited the book as a formative influence, claiming he’s spent his entire career essentially riffing on its central narrative device. “There is a monster at the end of all of my novels,” Parks told The Washington Post, “and I want you to feel this unbearable compulsion to turn pages and find out what it is.”

David Burr Gerrard, author of the literary sci-fi novel The Epiphany Machine and an instructor at the Yale Writers’ Workshop, was also mightily impressed by Stone’s slim tale. In an essay for Literary Hub, Gerrard wrote that The Monster at the End of This Book "formed [his] sense of what literature could and should do,” and later served as a gateway book to the works of Franz Kafka and James Joyce.

“I suspect The Monster at the End of This Book is one of those influences many thriller writers have in common, even if we’re not aware of it,” Riley Sager, the New York Times bestselling author of Home before Dark and the upcoming Survive the Night, tells Mental Floss. “It was certainly my first encounter with suspense—knowing from the title that there’s a monster waiting for us on the last page and feeling both dread and delightful anticipation as I made my way through the book—and of experiencing a twist ending. In hindsight,The Monster at the End of This Book acts as a sly commentary on the sometimes cruel curiosity humans possess. Grover implores us not to turn the page. Yet we do. Every damn time. Which, in a twisted way, makes us monstrous as well.”

8. The Monster at the End of This Book inspired several sequels, a popular app, a Twitter redux, and an animated special.

Stone and Smollin collaborated on several more Grover books following the success of The Monster at the End of This Book, starting with Hide and Seek with Lovable, Furry Old Grover in 1976 and continuing with Lovable Furry Old Grover’s Resting Places (do note the plural) in 1984. The pair produced a direct sequel in 1996 with Another Monster at the End of This Book, which features Elmo in a co-starring role. Please Do Not Open This Book, an interactive version that added flaps and pull tabs to Stone and Smollin’s original classic, was published in 2006.

The book has been translated into other media as well. An award-winning interactive app released in 2011 has been downloaded more than a half-million times. In 2013, the official Sesame Street Twitter account warned followers not to retweet “There Is a MONSTER at the End of This Twitter Conversation,” and an animated special called There Is a Monster at the End of This Story premiered in October 2020 on HBO Max.

Do you love reading? Are you eager to know incredibly interesting facts about novelists and their works? Then pick up our new book, The Curious Reader: A Literary Miscellany of Novels and Novelists, out May 25!