He is the world's most famous bottom-dweller — and now Hollywood is soaking up Nickelodeon's little sponge that could.

The denizens of Bikini Bottom and the stars of the wildly popular TV cartoon "SpongeBob SquarePants" (search) hit the big screen this weekend in "The SpongeBob SquarePants Movie." (search)

"This movie is really SpongeBob's big adventure," said series creator Stephen Hillenburg, referencing the first movie of another nerd character, Pee-Wee Herman.

For those not already in the know, SpongeBob is a jolly, porous, yellow kitchen sponge who lives in a pineapple under the sea — in a whimsical town called Bikini Bottom, next door to a grumpy squid. He also absolutely adores his job as a fry-cook, flipping Krabby Patties at the Krusty Krab fast-food shack.

"SpongeBob's job is to just be positive and think that every day is going to be the best day ever," said comedian Tom Kenny, who does SpongeBob's voice. "The people around him either find that delightful or ... just irritating."

Most half-hour SpongeBob TV episodes are made of 10-minute shorts, so the new 90-minute film required a different kind of story: Optimistic-yet-clueless SpongeBob and his slowwitted starfish friend Patrick travel to the surface to rescue the crown of temperamental King Neptune, voiced by "Arrested Development" star Jeffrey Tambor (search).

"You don't have to be bald to do this role, you have to be good to do this role," Tambor, who in real life is as bald as his character in the movie, told FOX News.

"SpongeBob SquarePants" has been the top-ranked Saturday morning cartoon for almost three of its five years on Nickelodeon. And it's not just kids watching. Of the 57.8 million people who watch "SpongeBob" every month, some 13.1 million are teenagers, and an amazing 20.4 million are adults, aged 18-49.

But why?

"It's about keeping your kid-nature in life and not totally becoming a curmudgeon," Hillenburg said. "As we get older it gets harder to do that."

Associated Press film critic Christy Lemire said the film is just as bright and colorful as the animated Nickelodeon TV show, but not as quick.

"By extending the premise to a 90-minute feature, 'The SpongeBob SquarePants Movie' feels dragged out and slowed down," said Lemire, who gives it two stars out of four.

Lemire also said some parts might be too scary for very young children — but most of them will go mad for it.

"They'll love the movie, then they'll demand to have it in their homes when it comes out on DVD," she warned.

FOX News' Mike Waco, The New York Post's Russell Scott Smith and The Associated Press' Anthony Breznican contributed to this report.