March 8, 2011; Source: Reuters | If, as expected, Bill Gates fails to regain the number one slot on the Forbes list of the world's billionaires scheduled for release Wednesday, he has no one but himself to blame. In fairness, though, he didn't lose the "richest man in the world" title, which he'd held until 2010 for most of the previous 14 years. Instead, he gave it away by choosing to endow the Bill and Melinda Gates Foundation with one-third of his personal wealth.

The Microsoft co-founder is now worth about $49 billion, which puts him behind Mexican tycoon Carlos Slim, whose fortune is estimated at $60 billion. Had he not given his money away, Gates would be worth closer to $88 billion today, according to Reuters. "It wouldn't be a competition," said David Lincoln, director of global valuations at wealth research firm Wealth-X. "(Gates) would have a comfortable margin if he had never discovered philanthropy."

For now, Sims' title seems safe, especially considering that he hasn't signed the "Giving Pledge," an effort being pushed by Gates and his billionaire friend Warren Buffett to get the ultra wealthy to publicly pledge to give away at least 50 percent of their wealth during their lifetimes or upon their death. According to Reuters, "Slim has said businessmen do more good by creating jobs and wealth through investment, "not by being Santa Claus," and while he has still pledged several billion dollars to charity, his efforts have been a fraction of Gates's philanthropy.—Bruce Trachtenberg