The creators of "Avatar: The Last Airbender" say that the new spinoff series "The Legend of Korra" will be more mature than the original show, but will still have the same sense of fun and adventure.

Nickelodeon, the network behind the original show, today announcedthat it will air the "Avatar" spinoff series "The Legend of Korra" (a working title) starting next year.

The...