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 claims to be the best of the best and has the typical smug attitude, known by having fangirls and a fanclub to go along, but, as the Anime moves forward, he becomes less prideful and arrogant than that of his earlier appearances in the anime.
Blastoise was chosen by Gary as his starter Pokémon. It evolved, and was used in the Indigo League against Ash's Charizard.
Gary is the counterpart of Green in the Japanese Edition of the manga, Pokémon Special. Though, due to the fact that Pokémon 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 shows nervousness when Mewtwo uses psychic powers on Arcanine and Nidoking.