Gary Oak, known in Japan as, in honor of the famous game designer Shigeru Miyamoto, is a fictional character in the Pokémon franchise. He is Professor Oak’s grandson and Ash Ketchum’s archrival in the "Pokémon" anime. He is usually seen in the anime with messy brown hair, wearing a purple sweater and a yin-yang pendant. In the video games, he is seen in both the outfit mentioned above, and a clothing style that features cargo pants and a black t-shirt. Wikipedia
The definitive Wikipedia entry for Gary Oak. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Gary_Oak