Stephen Hillenburg, the creator of the megahit Nickelodeon cartoon series SpongeBob SquarePants, has unfortunately passed away late Monday night. He was 57.

The cause of death was ALS, which Hillenburg revealed he had been diagnosed with 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.”

Hillenburg is a 1984 graduate of Northern California’s Humboldt State University and earned a bachelor’s degree in Natural Resource Planning and Interpretation, with an emphasis on marine resources. His animation career began in 1987 when he enrolled as a student at the California Institute of Arts in Valencia. He graduated in 1992 with a degree in Experimental Animation.

He began his partnership with Nickelodeon as a director and writer on the cartoon series Rocko’s Modern Life from 1993 to 1996. It was there that he created SpongeBob SquarePants, which eventually premiered on the network in May 1999. The series — which has won multiple awards, including honors from the British Emmy Awards, Annie Awards and ASACP Awards — has aired more than 250 episodes in its nearly two decades on air.

Hillenburg also wrote, produced, and directed The SpongeBob SquarePants Movie, which was released in 2004 and went on to gross over $140 million worldwide. Hillenburg then wrote the story for and was the executive producer of the sequel, The SpongeBob Movie: Sponge Out of Water, in 2015. When he revealed his diagnosis of ALS, he promised fans everywhere that he would continue to work on Spongebob until he was no longer able to.

Hillenburg is survived by his wife of 20 years, Karen Hillenburg, son Clay, mother Nancy Hillenburg and brother Brian Kelly Hillenburg, his wife, Isabel, and nieces Emma and Hazel.

💛 We are sad to share the news of the passing of Stephen Hillenburg, the creator of SpongeBob SquarePants. Today, we are observing a moment of silence to honor his life and work. 💛 — Nickelodeon (@Nickelodeon) November 27, 2018