Steve Ballmer's $120 billion fortune makes him richer than Warren Buffett, Mark Zuckerberg, and Google's cofounders. The former Microsoft CEO can thank AI hype and a contract quirk.

• Steve Ballmer is richer than Warren Buffett, Mark Zuckerberg, Larry Page, and Sergey Brin.
• The former Microsoft CEO is worth $120 billion, thanks to his estimated 4% stake in the company.
• Ballmer isn't a founder or current boss, meaning he sticks it out among the top 10 billionaires.

Steve Ballmer is wealthier than Warren Buffett, Mark Zuckerberg, and Google cofounders Larry Page and Sergey Brin — even though he didn't found Microsoft, and stepped down as its CEO nearly a decade ago.

Ballmer's estimated $120 billion fortune ranks him sixth on the Bloomberg Billionaire Index. He's an anomaly among the top 10 men, who either started their flagship companies (Bill Gates, Jeff Bezos, Larry Ellison, Zuckerberg, Brin, and Page) or still run them today (Elon Musk, Bernard Arnault, Buffett.)