David Hasslehoff, more celebs mourn 'SpongeBob SquarePants' creator Stephen Hillenburg Andrea Mandell- bay usatoday.com-

The creator of "Spongebob SquarePants," Stephen Hillenburg died at 57 from ALS. He was truly number one. USA TODAY

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

ALS, or amyotrophic lateral sclerosis, is a rare terminal illness 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 biggest hit, and has aired for nearly two decades since 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 sad to share the news of the passing of Stephen Hillenburg, the creator of SpongeBob SquarePants," the children's channel tweeted Tuesday. "Today, we are observing a moment of silence to honor his life and work."