Bill Gates is back on top. On top of a mountain of cash, that is.

The 57-year-old Microsoft co-founder has reclaimed his place at the top of the list of the world's richest people. The former Microsoft CEO is now worth a net value of $72.2 billion, just nudging out former billionaire champ Carlos Slim, who's worth a net value of $72.1 billion.

According to Cnet, it came down to a $550 million difference.

Bloomberg's annual billionaire index put Gates ahead of Slim for the first time since 2007 thanks to a surge in Microsoft's stock, which hit a five-year high on Thursday, and a slimming down of Slim's América Móvil, the dominate telecom provider in Mexico.

Microsoft has been trending upwards, by 28 percent this year, thanks to its sales of business and server software.

Móvil's downward trend is thanks in large part to the Mexican government's push to break Móvil's market dominance. Slim's company holds 70 percent of Mexico's mobile phone subscribers, Bloomberg reports. The push has resulted in a bill, which is likely to pass, that would prohibit any one phone company from owning more than 50 percent of the phone market.

But Gates isn't just sitting on a mound of cash. He's giving a good deal of it away to his Bill & Melinda Gates Foundation, an organization seeking to stem polio, spur innovation in agriculture and make water more affordable to the world's populace. So far, he's donated $25 billion to the fund.

Other top-ranking billionaires include (in order) Warrent Buffet, Amancio Oertega, Ingvar Kamprad, Charles and David Koch, Larry Ellison and Christie, Jim, Rob and Alice Walton, among others. You can take a peak at the full list here.

While Gates may be the richest American alive today, he isn't the richest in history. That title goes to oil tycoon John D. Rockefeller, worth around $340 billion in today's money. The richest person in history was Mana Musa I, who ruled the Malian Empire from 1280 to 1337. His net worth, thanks to rich deposits of salt and gold, was roughly $400 billion.