Matthew Gray Gubler is not an FBI profiler, but he plays one on TV. On the long-running CBS program Criminal Minds, he stars as super-genius Spencer Reid, the youngest member of the FBI’s Behavioral Analysis Unit. And, in his life off the set, Gubler expresses his creativity through filmmaking, painting, and, most recently, writing and illustrating his first children’s book, Rumple Buttercup: A Story of Bananas, Belonging, and Being Yourself (Random House, Apr.), a hand-lettered and illustrated 136-page fable about a “weird,” lonely, and very self-conscious green monster.

The book was published on April 2 with a 50,000-copy first printing and became an instant number-one New York Times bestseller, snagging the top spot on the New York Times’s Middle Grade Hardcover list. To date, Random House has gone back to press twice for a total of 100,000 copies in print.

In Gubler’s tale, sensitive monster Rumple Buttercup is so certain that his green skin, “5 crooked teeth” and “3 strands of hair,” will frighten people, he stays underground—literally—living in a sewer. He only feels confident emerging under the cover of night with a banana peel hat on his head, until a chain of events helps him to discover that no one cares that he’s different, and to embrace his uniqueness.

“I think we all feel like Rumples!” Gubler said, assessing what may account for some of the book’s appeal to readers. In addition, he believes the unusual handcrafted look of the book may draw some people in. “I hand-made every centimeter of every page with love, including the barcodes and copyright page, and I like to think that the hard work and sincerity translates.”

Gubler credits a sweet treat with helping to spark his imagination where Rumple is concerned. “I love telling stories, and Rumple popped into my noggin a little while ago while I was eating mint chip ice cream and staring at a banister made of lacquered wood,” he recalled. “I grabbed some melted crayons and a stack of old blank journals, and wrote it all down. After spending time refining it, and making sure that every one of Rumple’s expressions was just right, I was off to self-publish, but someone talked me into showing it to professional publishing houses.”

According to Gubler, Random House quickly proved a good fit for his project, thanks to what he considered an exceptionally winning gesture at their first appointment. “The Random House publishers came to the meeting with banana peels on their heads, and I was immediately enchanted,” said Gubler.

His publishing team at Random House felt the love he put into his creation straight away. “From the moment we received Rumple Buttercup on submission, we felt there was something special here,” said Mallory Loehr, senior v-p and publisher at Random House Books for Young Readers. “There was just so much heart in Matthew’s drawings and the story he was telling, we knew it was a book that children would respond to,” she added.

Once the project officially moved ahead, “It certainly had us puzzling over the category to call it,” Loehr said of the book’s unusual format. “Was it a 100+ page picture book? Or a poetic novel for middle-graders? We felt the audience was pretty broad, and so we published with that in mind, always asking where would Rumple reach the largest group of readers, and the kids who most needed to hear its positive message of inclusivity and acceptance.” To that end, the Penguin Random House catalog lists Rumple under the Children’s Middle Grade Books category, with an “All” age-range designation.

As someone accustomed to being in front of the camera, it’s no surprise that Gubler has embraced his role as the book’s ambassador with gusto, donning a Rumple costume at events, including at bookstores and schools during a national tour last month that included stops in New York, Austin, and Los Angeles. “I’ve been dressing up in a giant handmade Rumple Buttercup costume and having the best time ever meeting all my fellow Rumples across America,” Gubler noted. “I’ve been told I gave myself a hernia from picking up too many people at some of the signing events, but it’s been entirely worth it and I’m getting a second opinion on Tuesday.”

National media support has included an April 9 appearance on CBS-TV’s The Talk and an in-person interview with kid reporters for Newsday. On the digital marketing front, official Rumple Buttercup videos got good traction on Random House Children’s Books’ social media channels and Gubler’s social media platforms. A cover reveal shared on Gubler’s Instagram and Twitter accounts reached his 3.7 million followers combined, and vaulted Rumple to the #1 new release spot on Amazon in January. Gubler did an April 2 Premiere LiveSigning via Facebook Live with his mother that now ranks as the fifth largest children’s/young reader LiveSigning of all time, with more than 500,000 impressions made.

And fans hoping for Rumple swag are in luck as well. The Random House marketing team created a branded retail and merchandising kit complete with a character easel and white board, and temporary tattoos. Another launch promotion, an online #RumpleRaffle Sweepstakes, ran throughout the month of April, and encouraged entrants to post photos of their own Rumple creations using the hashtag for a chance to win custom art by Gubler and a signed book.

Gubler the actor will wrap his role on Criminal Minds next year when the series’ final season airs during the 2019–2020 season (though filming is nearly done already). In the meantime, Gubler the author will appear at the National Book Festival in Washington, D.C. on August 31 and says he has already finished a “journal draft” of his next book. “It isn’t about Rumple but takes place in the same Gublerverse,” he explained. “And the idea for the Rumple Buttercup sequel just came to me in a dream; I couldn’t be more excited!”

Rumple Buttercup: A Story of Bananas, Belonging, and Being Yourself by Matthew Gray Gubler. Random House, $14.99 Apr. ISBN 978-0-525-64844-4