Tributes have been paid to SpongeBob SquarePants creator Stephen Hillenburg following his death at the age of 57.
Baywatch and Knight Rider star David Hasselhoff, who played a lifeguard in 2004's SpongeBob SquarePants movie, said it was a "shocking loss".
"Wow what a unique and fantastic character Steve created!" he tweeted.
Professional skater Tony Hawk also paid tribute on Twitter, thanking Hillenburg "for the shared laughs" he'd had with his children through the years.
Lori Alan, who voiced the character Pearl Krabs, called Hillenburg a "ridiculously gifted, humble, gracious and huge hearted man" in a tribute on Instagram.
"You left this world - the entire world - happier, kinder and full of joy," she added.
Brad Bird, director of the Incredibles films, said he first had discovered SpongeBob though his sons when they were loudly singing along to its theme tune.
"I came down to see what the ruckus was about and ended up watching my first episode. Many laughs." he wrote.
I first discovered SPONGEBOB through my sons, who were loudly singing along with the dopey & memorable theme song downstairs. I came down to see what the ruckus was about and ended up watching my first episode. Many laughs.— Brad Bird (@BradBirdA113) November 27, 2018
Many thanks, Steve Hillenburg. May you Rest In Peace. pic.twitter.com/3VNsxYJVXq
Butch Hartman, creator of animated series The Fairly OddParents, called Hillenburg an "immensely talented creator" who would be "sorely missed".
Nickelodeon, which has broadcast the hugely popular cartoon series since 1999, confirmed Hillenburg's death on Tuesday.
In a statement, the company said the cause of death was motor neurone disease (also known as ALS), a condition he revealed he had been diagnosed with in March last year.
As well as creating the character, Hillenburg also directed 2004's The SpongeBob SquarePants Movie.
"We are sad to share the news of the passing of Stephen Hillenburg, the creator of SpongeBob SquarePants," Nickelodeon tweeted.
The channel said it would be observing "a moment of silence to honour his life and work."
The company's statement added: "Steve imbued SpongeBob SquarePants with a unique sense of humour and innocence that has brought joy to generations of kids and families everywhere.
"His utterly original characters and the world of Bikini Bottom will long stand as a reminder of the value of optimism, friendship and the limitless power of imagination."
SpongeBob fans have posted tributes on social media, thanking Hillenburg for "enriching lives" and "stirring up laughter for years to come".
Stephen Hillenburg, the Mayor of Bikini Bottom and all things SpongeBob, drifted into the great sea of beyond yesterday. Swim in Peace. He enriched lives and stirred up laughter for generations to come. What more could one person hope to accomplish. pic.twitter.com/PFvhZiJxqb— Exhibitor Relations Co. (@ERCboxoffice) November 27, 2018
Hillenburg is survived by Karen, his wife of 20 years, and son Clay.
The SpongeBob SquarePants series has seen more than 200 episodes broadcast and has spawned two successful animated films.