The episodes of SpongeBob SquarePants, an American animated television series created by marine biologist and animator Stephen Hillenburg (pictured) for Nickelodeon. Since its debut on May 1, 1999, 268 episodes of the series have been broadcast; its ninth season premiered on July 21, 2012. The series is set in the fictional underwater city of Bikini Bottom, and centers on the adventures of SpongeBob SquarePants (Tom Kenny), an over-optimistic sea sponge that annoys other characters. Many of the ideas for the show originated in an unpublished, educational comic book titled The Intertidal Zone, which Hillenburg created in 1984. He began developing SpongeBob SquarePants into a television series in 1996 upon the cancellation of Rocko's Modern Life. SpongeBob SquarePants has been noted for its appeal towards different age groups. During the second season, it became Nickelodeon's No. 2 children's program, after Rugrats. Nearly 40 percent of its audience of 2.2 million were aged 18 to 34. In season three, SpongeBob SquarePants passed Rugrats and earned the title of being the highest rated children's show on cable.