The world was introduced to SpongeBob SquarePants on May 1, 1999, but Stephen Hillenburg had developed these characters many years prior. Below is an early test of SpongeBob and Squidward's voices from 1996, as performed by Tom Kenny and Hillenburg, respectively.
In college, Hillenburg studied marine biology with a minor in art. In 1984, he began working at the marine science education organization Ocean Institute and his passion for the sea increasingly flowed into his art. An early version of SpongeBob SquarePants appeared in a comic book series Hillenburg developed called "The Intertidal Zone," that the institute used to teach visiting students about the diverse animal life inhabiting tide pools. The comic showcased a range of anthropomorphic sea creatures, many of whom evolved into the residents of Bikini Bottom.