SpongeBob SquarePants is one of the most polarizing figures in cartoon history. Some find the Nickelodeon character annoying and can’t stand his irritable laugh, while others think he’s the most adorable creature in all the seven seas. Love him or hate him, the porous yellow sponge (voiced by Tom Kenny) has, over a long TV life, become one of the biggest and most influential cartoon franchises. But the journey hasn’t been easy, especially with controversial accusations about SpongeBob’s presumed homosexuality and his ambiguous relationship with his best friend. (Show creator, Stephen Hillenburg, eventually came out and said SpongeBob is actually asexual.) Nevertheless, the show has endured and continues to be a staple on Nickelodeon, so much so that it’s hard to imagine a time when we didn’t know who lived in a pineapple under the sea.

It’s been 15 years since we were first introduced to the nautical world of Bikini Bottom and its cast of lovable sea critters. Hillenburg was working on cult classic, Rocko’s Modern Life, the adult-humored story of Rocko the wallaby dealing with life and its many dilemmas, when the first bricks of what would become SpongeBob SquarePants were laid down. Hillenburg, a marine biologist, created a comic in 1989 called The Intertidal Zone, where a sea sponge named Bob served as a host to talk about sea life. Some of the other characters included a sea star and a shore crab, who Hillenburg ultimately incorporated into the cartoon.

After Rocko’s cancellation in 1996, Hillenburg decided to pitch SpongeBob SquarePants, and enlisted help from former RML colleagues Derek Drymon and Nick Jennings to write and animate, respectively. The show was taken to Nickelodeon, where executives loved it and immediately gave it the greenlight. Nick gave Hillenburg and company some money and two weeks to craft a pilot. The result? “Help Wanted; Reef Blower; and Tea at the Treedome,” which premiered fifteen years ago today, on May 1, 1999.  

Viewers first encounter Sandy Cheeks, Bikini Bottom’s resident mammal and Texas tough squirrel, during “Tea at the Treedome,” when SpongeBob spots her outfitted in a space suit and wrestling a giant clam while he’s on a jellyfishing excursion. At first, Sandy seemingly defeats the giant clam, But then it resumes the attack, prompting SpongeBob to rush to her rescue, saying, “Hold on, little squirrel.” But this is Sandy we’re talking about, so she’s the one who actually does the rescuing. Audiences get their first glimpse of the show’s subversive nature when Sandy turns the tables on SpongeBob's rescue and lays waste to the “damsel in distress” trope. In a later episode, Sandy reaffirms her independence, saying, “SpongeBob, don't you worry about me. I can take care of myself. After all, who's the strongest critter in Bikini Bottom?”

One of the reasons SpongeBob SquarePants is the longest-running Nick toon is because of its mass appeal to kids, but also adults, given its RML roots. Rocko's Modern Life appealed to an adult audience with its sexual innuendos and social criticism. We see RML’s influence in the controversial and subversive topics SpongeBob SquarePants often tackles. Behind all the naive, good-natured fun, there’s a thoughtful exploration of more profound topics found under the sea.

When creating Sandy, Hillenburg says he wanted "a strong female character that could be a friend to SpongeBob but not a love interest." This echoes the strong female sensibility of  RML’s character Dr. Paula “Hutch” Hutchison. (She eventually becomes a love interest for Filburt, but is developed as a character before.) Hutch is a cat who loses her right hand, er, paw, in an accident and gets it replaced with a hook. Instead of being restrained by her disability she’s able to move on with her life. She’s a career woman! Hutch is a professional surgeon, veterinarian, and pediatrician. Having a female character with a career-oriented job is unusual,even more unusual is that it’s in the typically male dominated STEM (Science, Technology, Engineering,Mathematics) field. Sandy is a scientist and equally as brilliant, but she edges out Hutch because she’s both mentally and physically strong.

Hillenburg, cognizant of gender disparity, often confronted patriarchal situations. In one episode SpongeBob coaches Gary, his pet snail, for a race, and says, “Looks like training is gonna start early, ladies. I called you a lady to humiliate and demean you. It's a motivational tool we coaches use.” The scene cuts to Sandy elsewhere in Bikini Bottom saying, “Hmm. I don't know why, but I think I'll kick SpongeBob's butt tomorrow.” Not exactly revolutionary, but a child can understand that what SpongeBob said was wrong (and inaccurate) and that’s why Sandy proceeds to kick his butt at the end of the episode.

The show is able to freely examine themes of gender and sexuality because of its childlike nature. Because SpongeBob and his friends exist in a liminal space between kids and adults, they’re able to get away with playful subversions like crossdressing. But beneath the play, there’s something more.

Patrick Star, starfish and lazy best friend to SpongeBob, wears women’s clothing in “That’s No Lady” to conceal his identity. (He thinks he’s in danger.) Patrick gets a makeover and becomes Patricia, a lipstick-wearing, pigtailed blonde in a crop top and mini-skirt, whom Squidward and Mr. Krabs fawn over. SpongeBob has worn drag before as well. Patrick’s experimentation was for survival, but other instances—like the times SpongeBob wears Coral Blue semi-gloss lipstick no. 2—become examples of gender as performance. Always a smart, good thing to see on TV.

One episode that’s especially crucial to the show’s history of challenging societal norms is “Rock-a-Bye Bivalve.” The episode centers around SpongeBob and Patrick adopting a baby scallop. Throughout the episode, viewers see traditional gender roles in action, with SpongeBob assuming the feminine role, donning hair curlers and a nightgown as he cleans, irons, and takes care of the baby. Patrick assumes the masculine role as breadwinner. The show plays with these stereotypes and subverts them, forcing audiences to reconsider their definitions of gender in order to see it as a social construct. Just because SpongeBob takes on a “mom” role and dresses the part doesn’t mean he’s suddenly biologically female.

Hillenburg also shows subversiveness by subtly challenging the idea of the nuclear family in showing this faux family with two male figures. He isn’t outright advocating for gay parents, but he’s incepting the idea of different families that don’t to subscribe to the Leave It to Beaver norm. This is also evident with Mr. Krabs, SpongeBob’s cheapskate boss. He’s a crab, and single father to his presumably adopted whale daughter, Pearl.

It's tough to sort SpongeBob SquarePants into any category of the TV realm because of its complexity. In part, it's a kids show because it's on Nick (though at one point Spike TV wanted to buy the show and repurpose it to target adults like the animated adult show Ren & Stimpy), but it's often more mature than it seems. During his time as showrunner, Hillenburg was able to create a sort of middle-ground for the show to grow on and into.

SpongeBob SquarePants is more subliminal in its messaging in comparison to predecessors like Rocko's Modern Life and current shows like Adventure Time. Think of “Canned” when Rocko gets fired and works a series of jobs to make ends meet, including a phone sex operator; a sign behind him reads “Be Naughty.” Adventure Time also doesn't hide its adult themes. One of the series’ salient and compelling episodes, “I Remember You” reveals a past friendship between the Ice King and Marceline as he protects her after the Mushroom War, which many viewers thought of as a metaphor for World War II because of the mushroom cloud created by the atomic bomb.

SpongeBob’s resonance keeps the series afloat. Its childlike curiosity has fueled its boundary-pushing and subversiveness. The show’s characters, as well as the show itself, have struggled with identity, caught between finding humor in silly jokes and dealing with more mature things that come with growing up. In this way, the show is a representation of growing up.

As the show discovers new things, it will undoubtedly continue to push boundaries. If we’re lucky enough, SpongeBob SquarePants and his cast of undersea buddies will stick around for another 15 years.

Debbie Encalada is a '90s baby who thinks about Nickelodeon more than the average person. She tweets here

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