Squidward J. Q. Tentacles (born October 9) is one of the ten main characters of the SpongeBob SquarePants franchise. He is SpongeBob's and Patrick's grumpy neighbor and the former's coworker at the Krusty Krab who lives in an Easter Island head. He is a mostly unpleasant artist and musician, and his favorite hobbies are painting self-portraits and playing the clarinet.

Even though Squidward's name contains the word "squid," he is an octopus, not a squid, as confirmed in many interviews and episodes. He has the traits of an octopus—a round bulbous head and rectangular pupils—while a squid has a long triangular head and circular eyes, unlike Squidward. Squids have ten tentacles, many more than Squidward. The series' animators believed that giving him eight limbs would be too burdensome and difficult to animate, which is why he is usually depicted with six limbs. Notable exceptions are brief scenes in "Pressure" and "Sold!," in which he has a full set of eight legs. In "Feral Friends," his exact species is identified: a giant Pacific octopus.

He is a very cynical, selfish and a stick-in-the-mud individual. He works as the cashier at the Krusty Krab, a job he usually hates. Squidward is frequently annoyed by SpongeBob's loud and cheerful behavior, but he sometimes sticks up for SpongeBob and sees him as a friend. He can also have a supportive side for his boss on occasion.

More facts here: https://spongebob.fandom.com/wiki/Squidward_Tentacles