Nickelodeon's "Avatar" (search) has come out of nowhere to become one of the hottest kids shows on TV.

Even Nickelodeon appears to have been taken by surprise by the anime-style series grabbing "SpongeBob"-worthy numbers.

The series, created by Michael DiMartino and Bryan Konietzko, premiered last February and immediately found an audience, becoming the top-rated kids show in primetime.

Some weeks, it's even finished ahead of "SpongeBob (search)" and "Fairly Odd Parents (search)" — which air in the morning — among school-age kids.

" 'Avatar' is action-adventure in a way we've never produced it before, since that was a nut we hadn't been able to crack," says Nickelodeon President Cyma Zarghami.

"It's anime-flavored but age-appropriate ... and takes into consideration the need for adventure and comic relief with great boy and girl characters and violence without the blood and gore.

"It's action without hard-core evil.

"The timing was right for a property that takes our audience in a completely different direction than 'SpongeBob,' a series that's rich with backstory — which is attractive to kids," says Zarghami.

The series revolves around Aang, a 12-year-old boy who's awakened from a 100-year sleep by Katara and her older brother, Sokka, who discover Aang encased in an iceberg.

It turns out that Aang is really the "Avatar," a noble spirit able to control the world — water, earth, fire and air — through martial arts and magic. Aang is accompanied by his huge flying bison, Appa.

The drama revolves around a century-old war into which the three characters are thrown — while Aang is pursued by Prince Zuko, whose sole goal in life is to capture the Avatar in order to win the love of his father.

"Avatar" ends its first season Friday, and Nickelodeon has ordered 20 new episodes for a second season, expected to premiere early next year.

Zarghami says she was surprised at the speed in which "Avatar" grew into a bona fide hit for Nickelodeon.

"I expected it to happen, but I'm not sure I expected it to happen quite so quickly," she says. "I think what's great about ['Avatar'] is that it's not a continuing story — you can miss an episode and not feel completely lost.

"That's one of the things that allowed our audience to get into the show quicker," she says. "It's rich-but-simple and can be understood.

"To have a runaway hit, you can't alienate 5- and 6-year-olds with too complex a story, and you don't want to turn off 10- and 11-year-olds with something too simple.

"What the creators have done with 'Avatar' is figured out a way to be true to the concept and still have enough to be dramatically different."