Squidward Tentacles is bald with greyish green skin, a large nose, and lives in a Moai which is also known as an Easter Island Head located between SpongeBob's and Patrick's residences. He also has a female snail named Snelly who only appears in one episode. He works as a cashier at the Krusty Krab, a job he despises. SpongeBob and Patrick consider Squidward their friend, but the feeling is not mutual. Squidward tends to be a downer, and is often pulled into embarrassing and awkward situations by Spongebob and Patrick. He does not like SpongeBob and Patrick because they annoy him and he thinks he is more mature than them. However, he does show concern for them in some episodes such as when Spongebob eats a pie bomb, Squidward thinks he will never see him again and feels extremely guilty. Squidward's hobby is playing the clarinet, though he is only sometimes good at it, listening to jazz, suntanning, making sculptures, and painting. His main rival is Squilliam Fancyson, his former band classmate and the richest squid in Bikini Bottom.

The series animators illustrated Squidward with six tentacles, believing that giving him the proper number for an octopus (eight) made him look too burdened. This is revealed in the pop-up commentary of the "Krusty Krab Training Video" on the Season 3 DVD.