The founder of Gree, Japan's largest social networking website (overtaking rival billionaire Kenji Kasahara's Mixi), faced off with Facebook's Mark Zuckerberg after setting up shop in California. Yoshikazu Tanaka has an estimated net worth of $1 billion.

They are currently on global expansion kick - working with Tencent, the largest Internet service portal in China. Stock is up 35% over the past year; 5 for 1 stock split last fall. Tanaka started out at Sony, then worked for fellow billionaire Hiroshi Mikitani at the online shopping site Rakuten. However, he left in 2004 to set up Gree at a tech incubator. The company name is inspired by American social psychologist Stanley Milgram's concept of "six degrees of separation." It eventually transitioned the site into mobile gaming to better compete with rivals.

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