Stephen Hillenburg, the creator of the iconic Nickelodeon cartoon series SpongeBob SquarePants, died on Monday, according to Variety. He was 57.

Hillenburg's death was caused by ALS, which he was diagnosed with last year.

“We are incredibly saddened by the news that Steve Hillenburg has passed away following a battle with ALS,” Nickelodeon​​​​ said in a statement. “He was a beloved friend and long-time creative partner to everyone at Nickelodeon, and our hearts go out to his entire family. Steve imbued SpongeBob SquarePants with a unique sense of humor and innocence that has brought joy to generations of kids and families everywhere. His utterly original characters and the world of Bikini Bottom will long stand as a reminder of the value of optimism, friendship and the limitless power of imagination.”

The first episode of SpongeBob aired on May 1, 1999, introducing its audience to a dish sponge living in the city of Bikini Bottom and working at a local burger joint run by a crab. The humor of the show attracted both children and adults to enjoy the adventures of SpongeBob with his friends Sandy (a spunky squirrel from Texas) and Patrick (a dumb starfish), and his neighbor/coworker Squidward (a grumpy, artistically frustrated squid). There are almost 250 episodes of SpongeBob to date.

For millennials especially, the nonsensical world of SpongeBob SquarePants continues to define a generation through countless hilarious and timeless memes.

Along with the series, Hillenburg wrote, produced, and directed The SpongeBob SquarePants Movie, which came out in 2004. He was also the writer and executive producer The SpongeBob Movie: Sponge Out of Water released in 2015.

Our condolences to Hillenburg's family. Thank you for giving us the porous yellow icon who lives in a pineapple under the sea.