With very few exceptions, children's entertainment is created by adults. Sometimes these creators might sneak in some suggestive or subversive content into comics and cartoons aimed at younger readers in an attempt to express their more mature sensibilities. Some things, however, you just can't fit into kids' shows no matter how clever or subtle you are about it. It's at these times when these cartoonists have to find separate outlets for their creativity, working on other projects intended for mature audiences only.

RELATED: 15 Movies, Comics, Books, And TV Shows Written By Someone Younger Than You

Hearing for the first time about the work of some of these artists, whose names are heavily associated with reminders of childhood innocence, might come as a shock, but it really shouldn't. Think about it. If you had to work with the content restrictions of making kid-friendly content, surely part of you would want to indulge in a little ultra-violence in your art every now and then, right? Alternately, there are times when artists known for grown-up content are given the opportunity to make something aimed at a younger crowd. If you liked these cartoonists' work when you were growing up, prepare to discover their other projectsthat you might not have known existed.

15 THE PROTO-POWERPUFF GIRLS

Cartoon Network's first batch of Cartoon-Cartoons were based on student films, but not all of these student films were originally intended for children. Case in point: Blossom, Bubbles and Buttercup's first appearance was in Craig McCracken's sophomore CalArts project Whoopass Stew! The Whoopass Girls in: A Sticky Situation. In that cartoon, the Whoopass Girls were created through an accident involving a can of Whoopass.

"Whoopass" was not an acceptable word to use on children's TV, so when Cartoon Network ordered a new short from McCracken the can of Whoopass became "Chemical X" and the characters were now the Powerpuff Girls. McCracken was surprised that The Powerpuff Girls took off as it did with children, saying that he expected the extent of its success would be that "college kids would watch it and there would be a few random T-shirts out there in the rave scene or in record shops."

14 THE TIMMVERSE

Bruce Timm's DC Animated Universe on TV has long been considered the high standard for superhero cartoons; a series that simultaneously introduced kids to the DC superheroes and pleased long-time adult fans. The DCAU pushed boundaries of what was appropriate for family entertainment, and the PG-13 director's cut of Batman Beyond: Return of the Joker arguably passed those boundaries. With the DC DTV movies beginning with 2007's Superman: Doomsday, families were no longer the market.

Timm produced or executive produced the PG-13 DC DTVs up through 2013's The Dark Knight Returns: Part 2. He returned in 2015 to write Justice League: Gods and Monsters. Then, in 2016, he wrote DC's first R-rated animated feature, Batman: The Killing Joke. It received negative reviews, and the PG-13 Batman and Harley Quinn a year later didn't get a much better reception. Ironically Timm's kids' shows are more mature than his recent adult work.

13 REGULAR SHOW

If you ever watched Regular Show and felt like the show's sensibility was better suited for adults under the influence than for the kids it was supposedly for, there's a reason for that. The characters of Mordecai, Benson and Pops first appeared in creator J.G. Quintel's student project 2 in the AM PM. Their debut appearances occur in the short film during an acid trip.

Quintel's more adult sense of humor should be well-served by his next project, Close Enough. As of this publication, the TBS adult cartoons does not have a premiere date, but a trailer makes it look like a natural follow-up to Regular Show. According to the network's press release, it "centers on a married couple juggling such everyday challenges as parenthood, friendship, ham theft, stripper clowns and choosing the right day care."

12 A DIGIMON WRITER'S DARKER DIGITAL WORLD

Digimon Tamers, the third season of everyone's favorite non-pocket-based monster collecting anime, is remembered for being unusually dark by the standard of kids' toy commercial shows, with a meta narrative and Lovecraft-inspired horror elements. Why did Digimon of all shows go this route? Blame and/or thank screenwriter Chiaki J. Konaka.

Konaka's credits range from other darker-themed kids' shows like Princess Tutu and the 2003 Astro Boy to the adult-oriented likes of The Big O and Hellsing. The most relevant of his works in comparison to Digimon, however, is Serial Experiments Lain. Both shows are about digital worlds and inspired in part by Alice in Wonderland. Unlike Digimon, Lain is absolutely not for children, a slow-paced and disturbing psychological horror mindscrew. It's one of the best anime series of the late '90s, however, and if you're an adult who grew up liking Tamers, it's worth a watch.

11 LILO AND STITCH DIRECTOR'S PIN-UP ART

Chris Sanders' and Dean Dubois' Lilo and Stitch was praised for not following the typical Disney style, and Chris Sanders' character designs were a big part of that. Nani is an attractive woman, but she's not forced into the same unrealistic beauty standards as other Disney heroines, she has muscle and a bit of chub and realistic proportions.

Looking at Sanders' personal art, he has a tendency to celebrate women like Nani, but in more... suggestive contexts. Most of Chris Sanders' DeviantArt page is classified as "mature content." He draws a lot of nude or partially nude women in pin-up poses, all in his distinctive curvy art style. He continues to post these while also working on family films like How to Train Your Dragon and The Croods.

10 STEVEN UNIVERSE CREATOR'S COLLEGE WORK

Before she became famous storyboarding for Adventure Time and creating Steven Universe, Rebecca Sugar was already getting attention in the indie comics and animation world. Her comic Pug Davis, written while she was a student at SVA, is now out of print, but Sugar occasionally posts art of the characters on her tumblr, and some fans have expressed hopes the series could be revived as a show on Adult Swim.

The first time Rebecca Sugar got the attention of the Cartoon Brew animation blog was in 2007 for her sensual fanart of characters from Terrytoons, Ratatouille and Ed, Edd, 'n Eddy. The livejournal she posted these drawings on has since been deleted, but rumor is they were actually part of the portfolio that got her hired at Cartoon Network (she drew the Eds very on-model).

9 ED, EDD, 'N EDDY'S DISTURBING PREDECESSORS

Lupo the Butcher is a three minute short film in which a butcher curses at a piece of meat he's cutting, accidentally cuts off his own finger, then gets completely dismembered until his severed head starts throwing out insults during the credits. The Brothers Grunt is... harder to summarize, but it's bizarre, disgusting, and MTV sincerely wishes you forgot all about it.

Danny Antonucci got his start in animation working on '80s Saturday morning shows for Hanna Barbera. Lupo was a clear statement of wanting to get as far away from that sort of content as possible. But after Brothers Grunt, Antonucci was feeling confined by doing nothing but "gross" and "edgy" work. So what did he create next? Ed, Edd, 'n Eddy, which became Cartoon Network's longest running children's show.

8 INVADER ZIM'S ANCESTOR

What were the executives at Nickelodeon thinking when they hired Jhonen Vasquez to make a kids' show? Those who grew up with Invader ZIM are grateful they did, if perhaps scarred for life. If ZIM was unusually violent and misanthropic for Nicktoon, though, its content is actually toned down from the comics Vasquez was making before his animated breakthrough.

Vasquez's claim to fame in the '90s was a comic miniseries called Johnny the Homicidal Maniac, and it's about exactly what you would think it's about based on the title. Other works of his include Squee!, a JtHM spin-off about a kid facing assorted horrors, and Fillerbunny, about a bunny being tortured by mad scientists while trying to fill up space in a short comic. Vasquez has expressed discomfort with the idea young ZIM fans going back to read his adult comics.

7 REN AND STIMPY-STYLE MUSIC VIDEOS

Most Ren and Stimpy fans remember the Spike TV Adult Party Cartoon, and most of them wish they didn't. Not every adult-oriented project by creator John Kricfalusi has been so terrible, however, and his best work since the original Ren and Stimpy run on Nickelodeon has been in music videos. His video for Björk's "I Miss You" is well-remembered as a peppy surrealist burst of nightmarish insanity. His video for Weird Al's "Close But No Cigar" is unusually raunchy by Al standards, but well-animated.

John K.'s regular partners in filthy musical absurdity have been Tenacious D, Jack Black and Kyle Gass' comedy rock band. He directed the videos for "F--- Her Gently," a crude video for an equally crude song, and "Classico," similarly dirty but better animated. Their funniest collaboration is the opening parody of the THX logo for the movie Tenacious D in The Pick of Destiny.

6 THOMAS THE TANK ENGINE AND SAUSAGE PARTY

Sausage Party, a raunchy R-rated comedy filled with graphic content, nonstop cursing, crude stereotypes and criticism of religion was about in-line with what you'd expect from an animated film written by Seth Rogen and Evan Goldberg. It is decidedly not what you'd expect from directors Conrad Vernon and Greg Tiernan.

Vernon's credits have all been family films at Dreamworks such as those in the Shrek and Madagascar series. While Tiernan did direct the cinematics for the M-rated game God of War, the majority of his directorial work has been on Thomas & Friends videos aimed at even younger kids than Vernon's credits. Tiernan's Nitrogen Studios animated Sausage Party. Tiernan also faced backlash as a boss over reports of him overworking and mistreating animators.

5 RALPH BAKSHI BEFORE MIGHTY MOUSE

fritz

Mighty Mouse: The New Adventures provided a wacky escape from the relative blandness of '80s comedy cartoons and kickstarted the careers of many great animators. It also went under fire for supposed drug references in the episode "The Littlest Tramp," even though no drug references were intended. There's a reason the angry moral guardian types might have been suspect of the show, that reason being creator Ralph Bakshi's previous not-so-innocent movies.

Bakshi's directorial debut, Fritz the Cat, based on the R. Crumb comic strips, was rated X on initial release, a first for an animated film. Subsequent films of his included Heavy Traffic, Coonskin and Hey, Good Lookin', all edgy satires absolutely not for kids. Even his first attempt at making a "family film," Wizards, featured a villain using Nazi propaganda films to brainwash his army and a fairy whose nipples kept popping out of her shirt.

4 DR. SEUSS' ADULT BOOKS

dr seuss

Much attention has been paid of late to Dr. Seuss' wartime cartoons, given their surprising relevance to current political situations. But those aren't the only works by the beloved children's author aimed at an adult audience. He drew more "after dark" cartoons for the book The Adult Companion, as well as various pieces of dirtier artwork, such as a naughty Horton piece which is a bit too risqué for us to show.

His fourth book, and his first for adults, The Seven Lady Godivas, was about seven nudist women. He meant it to be "hot," but in his art style it was purely silly, and it didn't sell well. Following the book's failure, Seuss was quoted as saying "Adults are just obsolete children, and the hell with them." His only other book for adults afterwards, You're Only Old Once!, was subtitled "A Book for Obsolete Children."

3 THAT'S NOT DONALD DUCK!

Carl Barks' Donald Duck and Uncle Scrooge comics are some of the most celebrated in the entire medium, cited as inspirations by talents ranging from Osamu Tezuka and Art Spiegelman to George Lucas and Steven Speilberg and used as source material for the Ducktales cartoons. He wrote comics for Disney from 1942 to 1966. After 1966, his independent artwork gets... interesting, would be one way of putting it.

You see, back in the '20s, before he started working for Disney, Barks drew racy cartoons for The Calgary Eye-Opener. Barks wanted to go back to making "hotter" art, but after almost three decades of constantly drawing ducks, that was all he wanted to draw. Therefore, he combined the two urges to create paintings of... HAWT ducks!?!

2 THE GOD OF MANGA (...EVEN THAT GENRE)

Osamu Tezuka is best known in the United States as the creator of Astro Boy and Kimba, the White Lion, but he made all sorts of manga and anime, not just kids' stories. His medical drama Black Jack, philosophical epic Phoenix, and historical series Buddha and Message to Adolf are fairly well known among manga fans. More obscure are some of his darker manga like Ayako and MW. In addition to every other genre he touched, Tezuka also pioneered animated adult features.

The Tezuka-produced 1969-1973 "Animerama" trilogy of A Thousand and One Nights, Cleopatra and Belladonna of Sadness combined literary plots, experimental animation -- and graphic hardcore cartoon sex scenes! The films predate the rise of hentai as a genre by a decade and critics consider them classier than most anime porn that followed.

1 IT'S A BIRD, IT'S A PLANE, IT'S... WAIT... WHAT?

shuster bondage

Superman, pursuer of truth and justice, fought mobsters. His co-creator Joe Shuster, however, found himself writing comics for one. Really. Down on his luck, losing his eyesight and a legal battle for the rights to his greatest creation, Shuster needed whatever money he could get, so he ended up anonymously drawing the Night of Horror bondage comics for a mobster-turned-pornographer.

These comics were alleged to inspire the crimes of the "Brooklyn Thrill Killers." This led to an obscenity trial going all the way to the Supreme Court, ending in a ruling that pornography was not protected by the First Amendment. The comics were burned and the publisher arrested. Some copies still circulated around used bookstores, and comics historians figured out the art was Shuster's work. This history is detailed in Craig Yoe's book Secret Identity: The Fetish Art of Superman's Co-Creator Joe Shuster.

Can you think of any other "grown up" projects worked on by kids cartoon creators? Let us know in the comments!