Gary the Snail

The characters in SpongeBob SquarePants were created by artist, animator, and former marine biologist Stephen Hillenburg. In addition to the series' main cast, various celebrities have voiced roles in SpongeBob SquarePants. Notably, Ernest Borgnine and Tim Conway voice the roles of recurring characters Mermaid Man and Barnacle Boy respectively (Joe Whyte assumed the role of Mermaid Man shortly after Ernest Borgnine's death in 2012), while others have taken a cameo part.

Stephen Hillenburg conceived the characters for SpongeBob SquarePants in 1984, while he was teaching and studying marine biology at what is now the Orange County Ocean Institute. During this period, Hillenburg became fascinated with animation, and wrote a comic book titled The Intertidal Zone starring various anthropomorphic forms of sea lives, many of which would evolve into SpongeBob SquarePants characters, including "Bob the Sponge", who was the co-host of the comic and resembled an actual sea sponge as opposed to SpongeBob. In 1987, Hillenburg left the institute to pursue his dream of becoming an animator.

The characters of SpongeBob SquarePants have been well-received overall. The titular character SpongeBob has become very popular with children and adults. The character's popularity has spread from Nickelodeon's original demographic of two- to eleven-year-olds, to teenagers and adults, including college campuses and celebrities such as Sigourney Weaver and Bruce Willis. The popularity of SpongeBob translated well into sales figures. In 2002, SpongeBob SquarePants dolls sold at a rate of 75,000 per week, which was faster than Tickle Me Elmo dolls were selling at the time. SpongeBob has gained popularity in Japan, specifically with Japanese women. Nickelodeon's parent company Viacom purposefully targeted marketing at women in the country as a method of building the SpongeBob SquarePants brand. Skeptics initially doubted that SpongeBob could be popular in Japan as the character's design is very different from already popular designs for Hello Kitty and Pikachu. However, the characters have also attracted negative reception, including SpongeBob himself, who was listed as number four on AskMen's Top 10: Irritating '90s Cartoon Characters. Nevertheless, SpongeBob SquarePants was ranked ninth on TV Guide's top 50 cartoon characters.

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