Michael Rubin, a Philadelphia native, has been playing hardball in business since he was just a teen. His early days were tumultuous to say the least. By the time he was 16, Rubin was more than $200,000 in debt. But he has more than recovered: At 41, Rubin is worth $2.7 billion.

Today, Rubin is hyper focused on growing his three e-commerce businesses: fashion flash sale site Rue La La, two-day delivery membership program ShopRunner and sports-team gear site Fanatics. He says e-commerce is still a young and rapidly growing industry that stands to be changed as dramatically by mobile as the Internet has changed e-commerce.

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