The characters in the American animated television series SpongeBob SquarePants were created by artist, animator, and former marine biologist Stephen Hillenburg. The series chronicles the adventures of the title character and his various friends in the fictional underwater city of Bikini Bottom. Most characters are anthropomorphic sea creatures based on real-life species. Many of the characters' designs originated in an unpublished educational comic book titled The Intertidal Zone, which Hillenburg created in 1989.