Squidward Tentacles is the tritagonist and anti-hero of the animated series SpongeBob SquarePants. He is an intelligent neighbor of SpongeBob SquarePants and Patrick Star, as well as the rude, disloyal and lazy cashier of the Krusty Krab restaurant. Despite this, he is also quite sympathetic, of course as his life is little more than a dismal failure, and he is constantly pushed to the brink of insanity by his annoying neighbors.
SpongeBob and Patrick consider Squidward to be their friend, but this feeling is not mutual. Squidward also has a passion and interest in reading, arts, and music, and is very fond of playing the clarinet, though no one considers him to be very good at it, the same for his artwork. Although he hates him with a passion, Squidward usually does show a side of kindness and compassion for SpongeBob at times and even respects him.
- In "Fools in April," Squidward gets annoyed with SpongeBob pulling playful and harmless pranks on people at the Krusty Krab, and pulls a very cruel and harmful prank on SpongeBob in retaliation. Squidward then laughs at him when he comes out of the trash, which makes SpongeBob run out of the restaurant sobbing hysterically, and the Bikini Bottomites turn on him. Squidward tries to apologize, but he is physically unable to apologize until the very end of the episode, where SpongeBob has the last laugh: all his friends were standing behind him in his house and witnessed Squidward's apology. As a result, Squidward suffers a mental breakdown and runs off back to his house laughing maniacally after shouting that he had just fooled them as well.
- In "Can You Spare a Dime?," Squidward accepts SpongeBob's offer to live in his house until he finds a new job. However, he takes advantage of SpongeBob's hospitality by lying in bed all day and essentially making SpongeBob his domestic slave, staying so long that theFrench Narrator quits and not even attempting to find a job. This eventually proves too much for SpongeBob who for one of the few times in the series becomes angry with Squidward, who soon begins aggressively giving Squidward obvious hints to get a job, which Squidward either doesn't notice or chooses to ignore. Eventually, SpongeBob confronts Mr. Krabs in an attempt to force him to give Squidward his job back, and in the process accidentally reveals that Mr. Krab's first "dime" (a stone-age wheel) was in his pants the whole time, and that Squidward did not steal it.
- In "Squidward, the Unfriendly Ghost," when SpongeBob and Patrick believe they have killed Squidward and that he is now a ghost, he takes advantage of this by making them his slaves. Eventually, SpongeBob and Patrick, after reading a magazine about the Flying Dutchman's death, get the idea that Squidward is being mean and angry because he was never put to rest. SpongeBob and Patrick attempt to bury Squidward, which ultimately brings him to confess that he is actually alive. However, SpongeBob and Patrick still think that Squidward is a ghost in denial and send him to the "great beyond" by trapping him in a bubble, which floats up into the sky where the pelicans are.
- In the episode "Grandma's Kisses," Squidward and the customers at the Krusty Krab ruthlessly tease SpongeBob for having a kiss on his forehead given by his grandma. At the end of the episode, it is shown that they have been spying on SpongeBob with his grandma through her house's window.
- In "Employee of the Month," SpongeBob and Squidward viciously compete with each other for the employee of the month award, both of them trapping each other in hopes of getting to work first.
- In "Funny Pants," SpongeBob's laughing annoyed him, so he told SpongeBob that he had a "laugh box" that would burn up if he laughed within 24 hours and could never laugh again. SpongeBob eventually thinks he lost his laugh and goes into "spiraling depression." which proves to be too much for Squidward to handle.
- In "The Splinter," Squidward tells SpongeBob that Mr. Krabs will have to kick him out for getting a splinter at work.
- In "Sponge-Cano!," He scolds everyone in the Krusty Krab and yells at SpongeBob for humming.
- In "Professor Squidward" Squidward says he is Squilliam, but the principal finds a real Squilliam and then Squidward was arrested and sent to jail.
- In "I ♥ Dancing," Squidward gets jealous that SpongeBob has an audition in a musical, and "teaches" him how to dance in order to steal the spot for himself, training SpongeBob to the point of exhaustion. While he wins, he is to star in Squilliam's musical, and is forced to train to perform a dance that SpongeBob had performed earlier, with Squilliam clearly planning to run him ragged just as Squidward had done to SpongeBob.
- In "Good Ol' Whatshisname," Squidward steals What Zit Tooya's wallet, ran a red light in front of a police officer, is arrested, and was sentenced to ten years in prison.
- In "The Lost Mattress," while retrieving the mattress, Squidward nearly threatened to murder SpongeBob, and then he used him and Patrick as "worm bait." However, Squidward becomes the worm's prey.
- In "Krusty Towers," He made several ridiculous requests with the purpose of driving Mr. Krabs crazy (though Krabs did have this coming).
- In "New Fish in Town," He dragged SpongeBob, Patrick, and Howard's homes down a trench.
- In "That Sinking Feeling," He tried to separate SpongeBob and Patrick by drawing a line, and later, he threatened them that if Squidward's house was not back to normal on the count of three, he will grind them into chum (kill them).
- In "Restraining SpongeBob," Squidward had a restraining order placed on SpongeBob to keep SpongeBob away from him. When Patrick began to annoy Squidward far worse than SpongeBob, he released SpongeBob, and added Patrick to said restraining order.
- In "Little Yellow Book," Squidward reads SpongeBob's work diary in front of the customers, which made SpongeBob sad. He sees that he has been known as a "diary thief," but does not feel be until his house was repossessed. Later, he even reads SpongeBob's personal diary. This behavior even upsets Mr. Krabs who is considered the secondary antagonist of the series.
- In "Don't Look Now," SpongeBob and Patrick saw a scary horror movie. Squidward pretends to be the Fisherman in order to play a cruel joke on them. As a result, SpongeBob and Patrick misinterpret the Fisherman eating Squidward, they in reality end up injuring Squidward.
- In "Yeti Krabs," Squidward arrogantly attacks the Yeti Krab when he thought it was Mr. Krabs wearing a costume and nearly puts Mr. Krabs, SpongeBob, and himself in danger.