Gary Oak is Professor Oak's grandson and Ash Ketchum's chief rival in Pokémon Red, Blue and Yellow. In Red and Blue, he will choose the starter Pokémon that is strongest against yours; in Yellow, he will take the Eevee before Professor Oak can give it to you. Then you get his Pikachu. His other false name is Blue.
Gary Oak
Background
'Gary Oak' (Japanese: オーキド・シゲル, Hepburn: Ōkido Shigeru), voiced by Yuko Kobayashi in Japanese and Billy Beach in English, is Ash's rival. At first, he was arrogant, but has since become more open-minded. He and Ash grew up together in Pallet Town and quickly became rivals after becoming Pokémon trainers. Like Ash, Gary collected Gym badges and then competed in the Kanto and Johto League tournaments. After losing to Ash in the Johto League, he decides to pursue a career in Pokémon research, impeding his rivalry with Ash. During Pokémon Diamond and Pearl, he travels to Sinnoh.
Pokémon Strategies
Gary's Pokémon strategies are almost exacly like Ash; he spends more time raising his pokémon in good technique and teaches them tough and cool moves, while Ash uses clever strategy during battle and teaches most of his pokémon tough and smart moves. Gary's pokemon endures tougher training as well and doesn't rely on luck and love as Ash does.
In the Games
In the games, namely Pokémon Red and Blue and Pokémon Yellow, he is known as Blue. Pokémon FireRed and LeafGreen he is also known as Blue. He is the main rival of those games and later becomes the Champion.
Known Pokémon With Gary (anime)
Blastoise, Arcanine, Rhydon, Pidgeot, Tyranitar, Executor, Heracross, Scizor, Umbreon, Electavire, Nidoking, Alakazam