He is a domesticated house pet with similar mannerisms to a cat, but has royal blood, as seen in the episode "Rule of Dumb." In "Rule of Dumb," the royal family tree proves that Gary and Patrick are cousins, as their fathers were brothers. His mannerism and affinity for the finer things in life in previous episodes foreshadows his royal blood, with the only exception being his dislike for baths.
In many episodes, it has been indicated that Gary has great intelligence (at least for a snail). In "The Secret Box," Gary responded to SpongeBob's question with "Meow-no." SpongeBob did not think much of it and replied, "Aww, what do you know? You're a snail!" SpongeBob did not recognize it as special, perhaps meaning that it was not the first time that Gary spoke. In "The SpongeBob SquarePants Movie," the Bikini Bottomites were chanting "all hail Plankton," while Gary chanted monotonously "meow, Plankton." In "Jellyfish Hunter," it is revealed that he pays the electric bill. He may even be more intelligent than all the main characters (excluding Plankton), which is hinted to in "Sleepy Time," where Gary spoke in his dream (that SpongeBob was rudely interrupting) and sounded very old and wise. In the episode "Tutor Sauce," Gary is shown to be a good driver, as he is able to drive through the most dangerous road in Bikini Bottom, with no issue whatsoever (except the cops stopping the boat). He had an extensive library, which is a possible metaphor for intelligence. This is not true in early episodes, where Gary acted no more mature than a real animal. But this could perhaps be a plot device initially seeking to mollify the viewer with the basic description and behavioral traits of a simple house cat only later going on to disclose a wealth of rich cultural and intellectual traits.
It is suggested that SpongeBob had Gary when he lived with his parents as a really young boy. The episode "Treats!" reveals that Gary was adopted. As seen in "Gary Takes a Bath," Gary can levitate and teleport, possibly meaning that psychic powers run in the Star family, as Patrick has psychic abilities. Gary did not appear again after "Help Wanted" until the episodes "Plankton!" and "Naughty Nautical Neighbors." Gary has been to many places including the large Bass Vegas.
Gary had a minor role in the episode "Atlantis SquarePantis." Gary appears wearing a party hat and blowing on a paper horn. Gary is also a very good musician, although he was not part of Squidward's band in the episode "Band Geeks." In "The Paper," he played Squidward's clarinet very well, and Squidward gets confused. In "Procrastination," Gary played the trumpet. In "Something Smells" Gary played the violin to make SpongeBob cry while chopping onions because SpongeBob told him to.
In "Once Bitten," Squidward made many Anti-Snail wooden logs. A log somehow got inside Gary's foot and he got a splinter. Gary went out of control because the splinter or log was uncontrollably painful, and Squidward was the first to get bit.
"The Thing" reveals that Gary attacked Squidward violently. When Squidward turned into the thing, Gary violently attacked Squidward again.
In "Patty Caper," when SpongeBob blames Gary for supposedly stealing the secret ingredient to the Krabby Patty, Gary describes another suspect—Squidward, and, based on the picture Patrick had drawn of him, Gary must think Squidward is very ugly. However, it is possible that Patrick is just not a good sketch artist.
In "Little Yellow Book," he bites Squidward's tentacle because he was saying the horrible words to SpongeBob, his owner.
The episode "All That Glitters" shows that Gary has a large diamond under his shell. However, episodes afterward do not show the diamond under his shell.
Also to illustrate Gary's antagonism towards Squidward, in "I Was a Teenage Gary," when SpongeBob answers the door, to Squidward, holding Gary, Gary hisses at him.
Despite his disliking for Squidward, there have been several peaceful moments between the two, such as Giant Squidward and Nature Pants.
Gary has arms as seen in "Have You Seen This Snail?," "The Gift of Gum," and "Grooming Gary."
In the Croatian dub, his name is Slavko.
According to "Gary Takes a Bath," "Rock-a-Bye Bivalve," and "Pet Sitter Pat," Gary can read because in "Rock-a-Bye Bivalve," he is seen reading the newspaper, and in "Gary Takes a Bath," he is seen reading a book called "Snail Jokes." He was also reading a book called "Snail Tails" to Patrick at the end of "Pet Sitter Pat," although due to Gary's lack of English, Patrick could not understand him, as explained when he said "'Snail Tails'? I thought it was called 'Meow Meow Meow.'"
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 "A Pal for Gary," SpongeBob calls him "Gerald," meaning that Gary is likely a nickname.
In the first episode, "Help Wanted," Gary's pupils are small red dots and his meow is much squeakier.
In "Plankton's Pet," SpongeBob reveals he adopted Gary at an animal shelter. "Treats!" supports this, but "Have You Seen This Snail?" contradicts the continuity.
He seems smarter than most of the main characters, including SpongeBob, Patrick, Squidward and Mr. Krabs.
In the online game Snail Bob 2, Gary appears on a sign as a gag. It is labeled "Cousin Gary," implying that Gary and Snail Bob are related.
According to a variety of episodes, Gary may be compared to a cat. His usual way of speech is by saying "meow." In "A Pal for Gary," in the part where the Nudibranch Seller shows a portrait of a cat near a Nudibranch and later on shows Puffy Fluffy violently reacting to Gary may be a hint to the fact that Gary has a resemblance to a cat. As first seen in "Dumped," Gary purrs like a cat.
Gary is Patrick's cousin.
It was revealed in the season 8 episode, "Treats," that Gary's full name is "Gary Wilson, Jr."
He has the fifth most appearances in the series.
"Meow Plankton" (The SpongeBob SquarePants Movie)
"Meow… No." ("The Secret Box")
"Meow" (regal-like) ("Rule of Dumb")
In "The Thing," "What Ever Happened to SpongeBob," "Grooming Gary," and "Balloons," Gary screeches like a cat.