LOS ANGELES  — 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 SpongeBob 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.

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."