SpongeBob SquarePants is an active, happy-go-lucky sponge, who lives in a pineapple under the sea, while his grouchy, miserably squid neighbor Squidward Tentacles lives in an Easter Island head. SpongeBob's other neighbor and best friend is a chubby, jolly, pink starfish named Patrick Star, who lives under a huge rock. SpongeBob and Patrick live on either side of Squidward in 127 Conch Street.
- Main article: List of SpongeBob SquarePants characters
- SpongeBob SquarePants — A very friendly, funny, and happy-go-lucky seasponge that loves jellyfishing. He works at the Krusty Krab as the fry cook. He is Patrick Star's best friend.
- Patrick Star — SpongeBob's best friend, a dim-witted, pink starfish. He is somewhat foolish, selfish and silly, but a very good friend of SpongeBob.
- Squidward Tentacles — SpongeBob's next door neighbor and co-worker at the Krusty Krab, where he is the cashier. Squidward is a smart, artistic and somewhat sociopathic octopus. He hates SpongeBob and Patrick, and openly displays his hatred towards them, not that they ever truly understood. He believes he is an amazing artist and clarinet player, but quite the opposite in reality.
- Sandy Cheeks — A clever Texas squirrel that has to wear an oxygen tank to breathe underwater. Inside her house she wears a purple and green frilly bikini, that some fish find indecent.
- Mr. Krabs — A crab that is in charge of the Krusty Krab restaurant, where SpongeBob works. He is addicted to money and is selfish and greedy. He is 68.
- Pearl Krabs — Mr. Krabs' teenage daughter. She is a whale who acts like a stereotypical American teenage girl. Her father thinks he's spoiling her when quite frankly he is doing the opposite.
- Gary the Snail — SpongeBob's pet, his only sound is a "meow", similar to a cat. In fact, he is considered to be a sea cat, like a worm is considered a sea dog.
- Plankton - Sea plankton, who is Mr. Krabs' arch rival. He intends on getting the secret Krabby Patty formula and putting the Krusty Krab out of business.
- Mrs. Puff — Widowed, husband captured and turned into a pufferfish lamp. SpongeBob's pufferfish boating teacher. Mrs. Puff is eager to get SpongeBob out of her class.
- Mermaid Man and Barnacle Boy — Old, retired and foolish superheroes who are adored by SpongeBob, Patrick, and members of the "Mermaid Man and Barnacle Boy" Fan Club.
- Larry the Lobster — Buff, good-looking and well-fit lobster, usually found at Goo Lagoon, Bikini Bottom's local beach.
- Perch Perkins — The Bikini Bottom TV Reporter.
- Princess Mindy — The daughter of King Neptune (she was revealed in The SpongeBob SquarePants Movie). Patrick seems to like her.
- Patchy the Pirate - The president of the Spongebob Squarepants fanclub, He hosts live-action segments.
There seems to be little continuity between the episodes, as the characters often meet a horrible fate, only for everything to be returned to normal in the end. Numerous examples are as follows:
- In numerous episodes, the Krusty Krab and sometimes the entirety of Bikini Bottom itself is completely destroyed seemingly beyond repair, usually due to a mishap caused by SpongeBob.
- In "Clams," Mr. Krabs is eaten (spare his head and left arm) by a giant clam.
- In "Squidward the Unfriendly Ghost," SpongeBob traps Squidward in a giant bubble and sends him to the surface, where he is swarmed by seagulls.
- In "Wishing You Well," Mr. Krabs, in an attempt to prove to SpongeBob that magic doesn't exist, wishes that he was steamed and served with melted butter, which comes true seconds later.
- In "Mermaid Man and Barnacle Boy IV," SpongeBob uses the gadgets in Mermaid Man's utility belt to shrink Bikini Bottom and its inhabitants down to microscopic size, much smaller than even Plankton.
- In "SquidBob TentaclePants," in a frantic attempt to physically combine himself with SpongeBob again in order to re-create the ultimate show business spectacle, Squidward meddles with Sandy's "Molecular-Separator Ray" in such a way that the resulting disaster leaves Squidward, Mr. Krabs, SpongeBob, Patrick, Plankton, Larry the Lobster, Sandy, Pearl, and Mrs. Puff eternally fused together into one giant life form.
- In "Stanley S. SquarePants," Squidward and Sandy move and do not return in the episode.
- In "The SpongeBob SquarePants Movie," there is a second Krusty Krab, known as the Krusty Krab 2.
- In "Hocus Pocus," SpongeBob turns Patrick into a jar of mayonnaise.
- In "Shell Shocked," Gary's shell breaks and he uses Mr. Krabs' head as a shell.
Other continuity errors include paradoxes such as someone saying that someone doesn't exist but that person does exist later or looks and personality of one person changes and other errors.
- In "Enemy In-Law," Mr. Krabs claims that the Krabby Patty formula has been passed down his family, yet in "Friend or Foe," it is shown that Mr. Krabs and Plankton invented the formula together purely by accident.
- SpongeBob is interchangeably shown both with and without a skeleton.
- In many episodes, the character Old Man Jenkins appears with many different personalities and histories.
- In many episodes, Bikini Bottom is either portrayed as a big city (Pizza Delivery, Pre-Hibernation Week), or a small town (WhoBob WhatPants?).
- Patrick, when he thought he was ugly in Something Smells, said "What is my sister going to think? Oh wait I don't have a sister..." and in Rule of Dumb, Patrick is the only child of Herb and Margie Star. However, the episode Big Sister Sam is named after and revolves around Patrick's sister Sam.
However, there does seem to be some continuity shown in some instances. Examples are:
- Mr. Krabs robot from "Imitation Krabs" appearing in "New Leaf", or the seven "Mermaid Man and Barnacle Boy" episodes.
- In "Wet Painters", it is shown that Mr. Krabs framed his first dollar. This is done during the events of "Friend or Foe?".
- In "Driven to Tears", Patrick references "Have You Seen This Snail?" by saying to SpongeBob, "Don't forget to feed Gary. Sometimes you forget to feed him".
- In "Whelk Attack" SpongeBob says "I've had the Suds ", referring to the episode "Suds".
- In Summer Job, by the way Mr. Krabs talks, it seems that a relation between him and Mrs. Puff in Krusty Love has broken up.
- In Driven to Tears, Patrick didn't get arrested for crimes he comitted and later got arrested for them in Good Ol' Whatshisname.
- Plankton could have been in jail long enough to forget the formula in The Spongebob Squarepants Movie.
Although bubbles are often seen throughout an episode, occurrences such as tears flooding a building, inhabitants drinking liquids from glasses, and bathtubs filled with what seems to be water all fracture the underwater setting.
SpongeBob SquarePants is the only cartoon to consistently make the Top 10 list in the Nielsen ratings, and is the first "low budget" Nickelodeon cartoon, according to the network, to become extremely popular. Low-budget cartoons had not previously garnered as much esteem as higher-rated (and higher-budgeted) shows, such as Rugrats. When SpongeBob aired in 1999, it gained a significant number of viewers in the ratings, eventually becoming more popular than Rugrats had ever been. SpongeBob follows other Nickelodeon shows that have attracted "older" followers, including: The Ren & Stimpy Show, Rocko's Modern Life, the Kablam! skits, Action League Now! and The Angry Beavers. Other shows have followed in this trend as well: Invader Zim, Avatar: The Last Airbender and The Fairly OddParents won a similar fan base when they aired in 2001, and the latter is now second only to SpongeBob in popularity, while the former was cancelled despite gaining a cult following. The show debuted in 1999, and during that time, DragonBall Z and Pokémon were still the biggest crazes. SpongeBob did not gain its popularity until around 2000, and it has remained popular since then. It has extremely high ratings on tv.com scoring an average of 9.0. SpongeBob SquarePants ranked 15 in IGN's Top 100 Best Animated Series, just five spots behind the top 10 list, but was able to place in the top 20. .