The following is a list of characters that have appeared in or have been mentioned in Welcome to Bikini Bottom!.
- Seth Hamm - an adolescent human boy who works as a waiter at the Krusty Krab.
- Caleb Hamm - a 12-year-old human boy who is the younger brother of Seth Hamm.
- SpongeBob SquarePants - a very friendly, funny, and happy-go-lucky sea sponge who loves jellyfishing and works at the Krusty Krab as a fry cook.
- Patrick Star - a dim-witted, pink starfish and the best friend of SpongeBob, Caleb and Seth. He is somewhat foolish and silly, but is usually loyal to his friends.
- Squidward Tentacles - a smart, artistic and somewhat sociopathic octopus who hates SpongeBob and Patrick due to their childlike behavior. He somewhat likes Seth and Caleb as a friend. He works as a cashier at the Krusty Krab.
- Mr. Krabs - a selfish and greedy crab who is addicted to money and owns the Krusty Krab.
- Gary the Snail - a snail who is SpongeBob's pet, he usually only says 'meow' but in the original series, he once barked for the holiday spirit of Opposite Day. He is considered a sea cat.
- Mrs. Puff - a pufferfish and SpongeBob and Seth's boating teacher. She is eager to get SpongeBob out of her class, however she doesn't treat Seth the same way despite the fact that he is best friends with SpongeBob, a co-worker of him, and lived with him for 5 episodes other than being his classmate.
- Plankton - a copepod who is Mr. Krab's arch-rival and former best friend who constantly tries to steal a Krabby Patty to scan its ingredients or stealing the Secret Formula itself to put the Krusty Krab out of business and make the Chum Bucket a famous eating establishment.
- Mermaid Man and Barnacle Boy - two very old, retired superheros unrealistically old (Barnacle Boy is 108 and Mermaid Man is likely a supercentanarian) who are adored by SpongeBob and Patrick despite the fact that they are now very old and really can't do very much anymore.
BIkini Bottomites Edit
- Fred Rechid - a brown fish who says "My leg!" a lot.
- Tom - a green fish that is no for chasing SpongeBob and Patrick while screaming "CHOCOLATE!" in the SpongeBob SquarePants episode, Chocolate with Nuts.
- Anchovies - regular fish that have no names and are anchovies.
- Evelyn - a pink fish who is the mother of Shubie.
- Nancy Suzy Fish - a grey fish who has dated or been married to Nat Peterson.
- Nat Peterson - a yellow fish who is known for being the only customer at the Chum Bucket that actually liked Plankton's food.
- Archie - a red fish.
- Nazz-Mimi - a tall blue fish who wears a red bikini.
- Monroe Rechid - a small orange fish who is the child of Fred Rechid.