Mexican businessman Carlos Slim Helú is believed to be the richest man in the world. As chairman of Teléfonos de Mexico, better known as Telmex (NYSE: TMX) and América Móvil (NYSE: AMX), Slim has substantial influence over the telecommunications industry in Mexico, and much of Latin America as well.

The past year has been good to Slim. In the spring, with an estimated net worth of $53.1 billion, he overtook investing guru Warren Buffett as the world's second richest person. By the end of the summer, Fortune reported that Slim's net worth had grown to $59 billion, allowing him to overtake Microsoft founder Bill Gates as the world's wealthiest person.

Carlos Slim's personal wealth grew by $12 billion during the year, and he also controls a $150 billion business empire. His family's holdings represented more than 5% of Mexico's 2006 gross domestic product, and Slim-controlled companies made up one-third of the $422 billion Mexican stock exchange.

With his political connections and business savvy, Slim has managed to fend off accusations of monopolistic business practices for years, but the hammer may finally be about to fall. A probe of Carlos Slim's empire by Mexican antitrust regulators is scheduled to ramp up in the new year. Will 2008 see his empire crumble?

Last week Microsoft's Bill Gates expressed regret about being the world's richest man. When I read this, I was reminded of the expression, "be careful what you wish for, you might get it."

Before launching into an analysis of how Gates could be toppled from his throne, it's worth noting that I've admired Microsoft and wondered whether it's lost its elbow room. I praised Microsoft's ability to adapt to change in two of my books, The Technology Leaders and Value Leadership. But in the last several years, Microsoft seems to have lost its mojo as I noted in these interviews by Red Herring and The Washington Post.

Here's a surprise. The biggest threat to Gates's top rank on the Forbes 400 comes not from the number two on the list, but from numbers 15 and 16. According to that September 2005 list, Gates's net worth totaled $51 billion. Berkshire Hathaway's Warren Buffett came in second at $49 billion. And he was followed by Microsoft co-founder Paul Allen ($22.5B), Dell's Michael Dell ($18B) and Oracle's Larry Ellison ($17B). Spots six through 12 were occupied by descendants of Wal-Mart founder Sam Walton, Microsoft CEO, Steve Ballmer, and heiresses from Cox Enterprises and Fidelity.