We’ve said goodbye to too many pop culture icons in 2018. Among them is SpongeBob Squarepants creator Stephen Hillenburg, whose smash-hit Nickelodeon cartoon has become a cultural phenomenon since it premiered in 1999. According to Variety, Hillenburg died from ALS at age 57, after receiving a diagnosis in March of 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.”

Variety reports that Hillenburg began his animation career in 1987, just 12 years before SpongeBob splashed onto the scene. He won an award for Best Animated Concept at the Ottawa International Animation Festival for his animated short “Wormholes” and worked on the Nickelodeon series “Rock’s Modern Life” as both a director and writer from 1993-1996.

To date, SpongeBob Squarepants has aired nearly 250 episodes. Hillenburg also wrote, produced and directed The SpongeBob Squarepants Movie, which premiered in 2004. He also wrote the story for and executive produced the 2015 sequel, The SpongeBob Movie: Sponge Out of Water.

In addition to winning both U.S. and British Emmy Awards, Annie Awards and ASACP Awards, SpongeBob Squarepants has been dubbed or sub-titled in more than 60 languages, has been adapted to comic books, and has spawned several toy lines, among other merchandise. Saying goodbye to the series’ creator just before its 20th anniversary is especially heartbreaking. May he rest in peace.