Stephen first revealed his ALS diagnosis in 2017. He's survived by his wife, Karen, and his son, Clay.
Nickelodeon called him "a beloved friend and long-time creative partner to everyone at Nickelodeon, and our hearts go out to his entire family."
Steve created 'SpongeBob' in the late '90s, but he took a circuitous route to his TV and movie success. Hillenburg started out teaching marine biology in Orange County ... but eventually combined that knowledge of ocean creatures with his artistic talent.
He broke into TV as a director and writer on the Nickelodeon show, "Rocko's Modern Life" -- and then eventually started creating his 'SpongeBob' ... which debuted in 1999.
In addition to the TV series, Steve wrote both hit 'SpongeBob' feature films. The first one grossed more than $140 million.
Variety first reported Hillenburg's death. He was 57.
Enjoy a Krabby Patty today in his name.