Gary has mahogany hair and black eyes. In the original series, Gary wore a long-sleeved purple shirt, a black necklace, dark blue pants and boots. In the Advanced Generation series and Diamond and Pearl series, he wore a black collared shirt, pants, a black necklace with a lavender bead instead of the original gold, and sneakers with a dark backpack.
The day he started out on his Pokémon journey, Gary came off as an arrogant Trainer, much like his game counterpart, Blue. His chosen starter Pokémon was Squirtle, which was actually the same Pokémon that Ash originally wanted to start with. He even had a group of cheerleaders who cheered him on in all of his battles and would go so far as crying whenever he lost. He didn't walk on his journeys like most Trainers did; instead he had his own sporty red convertible with a chauffeur. Gary loved when he got a chance to make fun of Ash by bragging about how far behind Ash was compared to him. He also gave Ash the pet-name of "Ashy-boy" (Japanese: "Satoshi-kun"), which occasionally seems to annoy him. His style of training at that point was to capture many Pokémon and to use the strongest, as a stark contrast to Ash, who focused on developing a bond with his Pokémon.
In his few appearances during the Johto saga, Gary seemed to have become the complete opposite of who he was. He became polite and respectful to others, including Ash.
Gary Oak is Ash's rival. He first appeared in Pokemon - I Choose You!, where he left Pallet Town and wanted to become a Pokémon Master before Ash did. In the beginning, Gary claimed to be the best of the best and had the typical smug attitude, known by having fangirls and a fanclub to go along, but, as the anime moved forward, he became less prideful and arrogant than that of his earlier appearances in the anime.
Gary is the counterpart of Blue in the Japanese Edition of the manga, Pokémon Special. Though, due to the fact that Pokémon Red and Green was not released in America, his name was changed to Blue in the manga and games for the English release.
Gary is shown to care about his Pokémon. Also, he is shown at least once kissing a Poké Ball before sending his Pokémon out. In the episode that this happened, The Battle Of The Badge, Gary showed nervousness when Mewtwo used its psychic powers on Arcanine and Nidoking.