Stephen Hillenburg, the visionary creator of “SpongeBob SquarePants” died Monday, Nickelodeon and Jessica Berger, a rep for his family, verified to USA TODAY. The cause of dying was ALS.

ALS, or amyotrophic lateral sclerosis, is a rare terminal sickness that affects nerve cells in the brain and the spinal cord. It’s also known as Lou Gehrig’s disease.

“SpongeBob” is Nickelodeon’s all-time largest hit, and has aired for nearly two a long time because its premiere on May 1, 1999, bringing characters SpongeBob, Patrick, Squidward, Mr. Krabs, Sandy Cheeks, Plankton, Pearl Krabs, Mrs. Puff and Larry the Lobster to life.

“We are unhappy to share the information of the passing of Stephen Hillenburg, the creator of SpongeBob SquarePants,” the kid’s channel tweeted Tuesday. “Today, we are watching a moment of silence to honor his lifestyles and work.”