Mark Zuckerberg is the best known of the four founders of Facebook, of which he is now CEO and chairman.

He began work on a social networking site while still studying computer science at Harvard, which soon evolved into Facebook. It had about 500 million users around the world by 2010 and is still growing, making it the world's biggest social networking site. Mark Zuckerberg now has personal wealth of over $12 billion.

That may be why he doesn't seem too worried that Facebook isn't doing so well on the financial markets. The company has never done well on the stock market, but Zuckerberg is now busy with a new project - creating a huge campus for the company in California. There will be space for over 3000 engineers, so he clearly has very big plans for the future of Facebook.

You can see a detailed biography of Mark Zuckerberg here.