SPONGEBOB SQUAREPANTS creator Stephen Hillenburg attends the world premiere of "The SpongeBob Movie: Sponge Out Of Water" in New York in January 2015.

LOS ANGELES (AP) — Stephen Hillenburg, who used his dual loves of drawing and marine biology to spawn the absurd undersea world of “SpongeBob SquarePants,” has died, Nickelodeon announced Tuesday.

Hillenburg died Monday of Lou Gehrig’s disease, also known as ALS, the cable network said in a statement. He was 57.

He had announced he had the disease in March 2017. His death comes just weeks after the passing of another cartoon hero in Marvel creator Stan Lee.

Hillenburg conceived, wrote, produced and directed the animated series that began in 1999 and bloomed into hundreds of episodes, movies and a Broadway show.

The absurdly jolly Sponge-Bob and his yell-along theme song that opened “Who lives in a pineapple under the sea?!” quickly appealed to college kids and parents as much as it did kids.

“The fact that it’s undersea and isolated from our world helps the characters maintain their own culture,” Hillenburg told The Associated Press in 2001. “The essence of the show is that Sponge-Bob is an innocent in a world of jaded characters. The rest is absurd packaging.”

Its vast cast of oceanic creatures included Sponge-Bob’s starfish sidekick Patrick, his tightwad boss Mr. Krabs, squirrel pal Sandy Cheeks and always-exasperated neighbor Squidward Tentacles.

While Hillenburg introduced and popularized exotic creatures like the sea sponge (which in the real world is not square,) Bikini Bottom was a realm like no other, real or fictional. SpongeBob can play his nose like a flute and could not possibly be happier to work his fast-seafood job of flipping Krabby Patties.

But he has his troubles, too. He constantly fails his boat-driving test, forcing his frightened blowfish teacher to inflate. In one episode he suffers a broken butt and is afraid to leave his pineapple home for days.

“I don’t want to face my fears,” SpongeBob, voiced by Tom Kenny, says in another episode. “I’m afraid of them!”

Born at his father’s army post in Lawton, Oklahoma, Hillenburg graduated from Humboldt State University in California in 1984 with a degree in natural resource planning with an emphasis on marine resources, and went on to teach marine biology at the Orange County Marine Institute.

While there he drew a comic, “The Intertidal Zone,” that he used as a teaching tool. It featured anthropomorphic ocean creatures that were precursors to the characters on “SpongeBob.”

Hillenburg shifted to drawing and earned a master of fine arts degree in animation from the California Institute of the Arts in 1992.

That same year he created an animated short called “Wormholes” that won festival plaudits and helped land him a job on the Nickelodeon show “Rocko’s Modern Life,” where he worked from 1993 to 1996 before he began to build SpongeBob’s undersea world of Bikini Bottom, which showed off his knowledge of marine life and willingness to throw all the details out the window.