Stephen Hillenburg, a onetime marine biology teacher who created the enduringly popular "SpongeBob SquarePants," an Emmy Award-winning animated Nickelodeon program about a goofy underwater world that was the defining cartoon show of its generation, died Nov. 26 at his home near Los Angeles. He was 57.

He had amyotrophic lateral sclerosis, or Lou Gerhrig's disease, said Susan Grode, a lawyer for the family.

Long fascinated by art and cartoons, Hillenburg turned to animation and in 1999 launched "SpongeBob" on the Nickelodeon network. The series, set underwater at Bikini Bottom, was relentlessly, even absurdly upbeat.

The title character was introduced in the show's theme song: "Absorbent and yellow and porous is he!" Resembling an ordinary kitchen sponge wearing shorts and a necktie, SpongeBob had big eyes, two teeth and oversized pair of shoes. He lived in a pineapple under the sea at a place called Bikini Bottom, with his pet snail, Gary, and was beamingly proud of his job making Krabbie Patties and the Krusty Krab eatery.

SpongeBob was surrounded by a zany cast of anthropomorphic creatures, including a pink starfish named Patrick Star; a squirrel named Sandy Cheeks who adapted to underwater life by living in a dome; Squidward Tentacles, a snobbish, clarinet-playing octopus; the cranky owner of the Krusty Krab, Mr. Krabs; and the diabolical Plankton, a villain constantly plotting to steal the recipe for Krabbie Patties, guarded by SpongeBob.

By replaying endless variations on these characters and themes - including SpongeBob's futile attempts to obtain a boating license from Mrs. Puff, a puffer fish - the show became a whimsical cultural phenomenon watched by tens of millions of viewers each week.

"It seems to be a refreshing breath from the pre-irony era," Syracuse University pop-culture scholar Robert Thompson told the New York Times in 2001. "There's no sense of the elbow-in-rib, tongue-in-cheek aesthetic that so permeates the rest of American culture . . . I think what's subversive about it is it's so incredibly naive - deliberately."

The program attracted fans among celebrities - Ellen DeGeneres, Bruce Willis and Jerry Lewis all admired its absurdist humor - and among college students, who reveled in the adult overtones that occasionally floated to the surface from Bikini Bottom.

In 2005, SpongeBob and other cartoon characters were featured in a promotional video promoting tolerance and diversity. Afterward, James Dobson, leader of the conservative activist group Focus on the Family, accused SponeBob and his cartoon pals of being a little fishy.

"Their inclusion of the reference to 'sexual identity' within their 'tolerance pledge' is not only unnecessary," he said, "but it crosses a moral line."

Hillenburg replied that tolerance was certainly a theme of the show, but the idea of sexuality had no connection to the innocent characters of "SpongeBob SquarePants."

"I consider them to be almost asexual," he said. "We're just trying to be funny and this has got nothing to do with the show."

This article was written by Matt Schudel, a reporter for The Washington Post.