He is a domesticated house pet with similar mannerisms to a cat, most notably his "meow," but has royal blood, as seen in the episode "Rule of Dumb." In the said episode, the royal family tree proves that Gary and Patrick are in fact cousins, as their fathers were brothers. His mannerism and affinity for the finer things in life in previous episodes foreshadow his royal blood, with the only exception being his dislike for baths.
It is suggested that SpongeBob has had Gary ever since he lived with hisparents as a really young boy. The episode "Treats!" reveals that Gary was adopted by SpongeBob.
Gary was the only child of Sluggo Star and an unrevealed mother.
At one point, he was adopted by SpongeBob at the local animal shelter. In "Treats!" a picture is shown of the moment SpongeBob picked him out, showing that Gary spent his early childhood at the pound with three other snails.
One day, Gary betrayed SpongeBob in exchange for Patrick, though this was only done to retrieve a cookie from Patrick's pocket, and Gary subsequently returned to his original owner.
At some point, Gary moved out of Bikini Bottom and into Bass Vegas in response to SpongeBob's unintentional negligence. He was thereafter taken in and sheltered by an elderly woman named Granny, who mistook him for one of her snails.
Once Gary discovered SpongeBob was looking for him and finding out Granny’s motive, he escaped her house and returned to Bikini Bottom to reunite with SpongeBob.
At various points, Gary has worked for the Krusty Krab, typically as a waiter  or a fry cook. At one point, he was hired to rid everyone of the ick contamination. At another point, he was hired as the restaurant's bouncer.
When SpongeBob made his own restaurant called SpongeBob's Place, Gary was hired as the cashier.
Gary is a sea snail with a pink shell decorated with purplish-blue spots and a red spiral. He has eye antennas that hold together his scarlet-green eyes with orange-red pupils. The sides of his body are light blue and his belly is green. He is typically known to create trails of slime when crawling. Even though he's seen without legs, "Your Shoe's Untied" reveals that he has legs and wears shoes.
Being a snail, which is to Bikini Bottom what cats are to the real world, Gary is only able to communicate by saying "Meow."
In many episodes, Gary has exhibited great intelligence. In "The Secret Box," Gary responds to SpongeBob's question with "Meow-no." SpongeBob does not think much of it and brushes off his remarks on account of Gary just being a snail, implying Gary spoke to him before. In The SpongeBob SquarePants Movie, the Bikini Bottomites are chanting "All hail Plankton," while Gary monotonously chants, "Meow, Plankton." His intelligence is best exhibited in "Sleepy Time" where his dream counterpart is revealed to own a library and has an extremely intellectual mindset, having the ability to cite literature. His wise demeanor is also shown in "Chatterbox Gary" where he exercises his sophisticated vocabulary to describe his owner and peers. In "Jellyfish Hunter," it is revealed that he pays the electric bill.
In "Once Bitten," he becomes aggressive and bites several of the Bottomites as a result of the pain that a splinter is inflicting. Even after said splinter is removed, Gary bites Mr. Krabs. However, this was done completely out of pain and/or habit.
In "The Thing," Gary viciously attacks Squidward despite him having done nothing wrong. However, this is common for pets to do.
In "Chatterbox Gary," Gary throws a walkie-talkie in Squidward's throat in retaliation for interfering with his translation collar. However, it was Squidward's fault in the first place.
He has a passion for animal rights and not being subject to things he does not want to do.
In "Grooming Gary," Gary joins the other pets in rioting against their respective owner for fancying his personality, which he did not want in the first place. However, this was done out of respect for himself and the other pets, who were being mistreated and shown off against their wills.
In "Gary Takes a Bath," Gary snatches a ladder away from the tree that SpongeBob is stuck in, eliminating his option to escape safely. However, this did not cause any true harm to SpongeBob, who simply fell in mud.
In "House Worming," Gary kicks SpongeBob out of his own home, although this was done out of self-defense.
Abilities and talents
Gary helps SpongeBob tie his shoes in "Your Shoe's Untied," revealing that he wears brown shoes on his feet that are hidden under his body.
As seen in "Gary Takes a Bath," Gary can levitate and teleport. Gary has been to many places, including the large Bass Vegas.
In the episode "Tutor Sauce," Gary is shown to be a good driver, as he is able to drive a boatmobile through the most dangerous road in Bikini Bottom with no issue whatsoever, except the cops stopping the boat.
Though Gary is intelligent and loves his owner, SpongeBob, he can be naughty at times, sometimes in his rivalry with Squidward.
In "Gary Takes a Bath," Gary refuses to take a bath, does nothing about a bomb strapped to SpongeBob's chest, and takes SpongeBob's ladder away, leaving him stuck on a tree.
In "Once Bitten," he becomes aggressive and bites just about every citizen in Bikini Bottom, even SpongeBob, and was accused of having "Mad Snail Disease," although these actions were purely caused by a splinter stuck in his body. Even after the splinter is removed, he bites Mr. Krabs.
In "The Thing," he viciously attacks "Smelly" after detecting his real identity.
In "Grooming Gary," he riots because SpongeBob, and other pet owners, had made him "fancy," which he did not want to be.
In "Treats!," he constantly bothers SpongeBob by asking him to get more Snail Bites, even going so far as to make him go to every pet store in the world to see if they have them.
In "Gary's New Toy," Gary becomes so distracted in his ball that he disregards SpongeBob whenever he needs him, though this is because the ball hypnotizes him. As SpongeBob tries to place the ball away from Gary, he manages to get it back. When it comes to the decision that SpongeBob tells Gary either him or the ball, Gary goes for the ball, leaving his owner to cry and live out on the streets. When Gary remembers SpongeBob leaving, he realizes the ball is evil and reconciles with SpongeBob.
Gary has had several episodes that center around him or relate to him:
"I Was a Teenage Gary": When SpongeBob has Squidward come to take care of him, Gary becomes starved and sick.
"Dumped": Gary runs away from home to be with Patrick in order to get the cookie out of his pocket.
"Gary Takes a Bath": Gary tries to escape SpongeBob's plans to get him to take a bath.
"The Great Snail Race": SpongeBob becomes a strict coach and is obsessed with winning the race trophy with Gary's poor body.
"Have You Seen This Snail?": Gary runs away from home after not being fed and Granny takes him in. He later finds out that SpongeBob is looking for him and that his new owner wants to feed him to death, so he escapes and returns to SpongeBob.
"Once Bitten": Squidward's anti-snail defense log affects Gary and he bites Bikini Bottomites, including SpongeBob, making them think that they are zombies.
"Fungus Among Us": Gary is the first one to make the solution by eating away the ick.
Gary rarely gets in injured in the show. He is mainly injured when he fights with other or evil pets and when SpongeBob is not around and there is no food (it was Patrick's fault who ate all of Gary's food due to his high lack of hunger), he might starve to death.
SpongeBob is Gary's owner and closest friend. SpongeBob often goes to Gary for advice when no else is able to help him. Although Gary often finds himself irritated by SpongeBob's naivety and falls victim to negligence and pressure by him at times, the two always get back on good terms in the end.
Gary has speaking roles in both of the SpongeBob movies. He plays a larger role in the first movie, appearing at crucial points (once to remind SpongeBob and Patrick of their friends suffering back in Bikini Bottom, and again at the end when SpongeBob frees him from his mind-control helmet).
"All That Glitters" shows that Gary has a large diamond under his shell. However, episodes afterward do not show said diamond under his shell.
Aside from his trademark "Meow," Gary can say the words "Plankton," "Yeah!," and "No!"
In the first teaser trailer for The SpongeBob SquarePants Movie, Gary is shown enjoying taking a bath with SpongeBob as the latter plays with his water toys, even though Gary is shown to hate taking baths.
It is revealed in The SpongeBob Movie: Sponge Out of Water that Gary hates mayonnaise.
The scene from "Help Wanted" in which SpongeBob wakes up and greets Gary originally ended with Gary taking a bite from a cactus, in reference to garden snails' tendency to feed on succulent plants. The book Not Just Cartoons: Nicktoons! features the original storyboard of this scene.
In the Croatian dub, his name is "Slavko."
Gary has many things hidden under his shell: a house, SpongeBob's Krabby Patty T-shirt, a record player, a diamond, and many other pieces of junk.
In "Help Wanted," Gary's pupils are small red dots and his meow is much squeakier.