'Gary Oak' (Japanese: オーキド・シゲル,Ōkido Shigeru), voiced by Yuko Kobayashi in Japanese and Billy Beach in English, 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.
Gary and Ash's techniques are like the North and South pole's of the world; while Gary spends his time raising his Pokémon in good technique and teaches them tough and cool moves, Ash uses clever strategy during battle and teaches most of his Pokémon tough and smart moves; Gary's Pokémon endure tough training and do not rely on luck and love in order to win battles.
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.
Gary, along with 3 other main rivals (Drew, Paul and Trip) all have their Japanese names start with"Sh-". Gary is Shigeru, Drew is Shuu, Paul is Shinji and Trip is Shooti.
There's an interesting coincidence regarding Gary and Ash's rivalry: the word "rival" is descended from the Latin word rivalis, meaning "one who shares or uses the same stream"; in the anime, the earliest point of Ash and Gary's rivalry (perhaps its origin) shows Ash and Gary fishing for Magikarp in the same stream.
Gary appeared during all Pokémon series. Since Best Wishes! started, it is assumed that he, Misty, May, Max, Dawn, Tracey, and Brock may not appear at all in the Best Wishes! series at all because of its fresh new start.