The former Microsoft CEO is worth $120 billion, thanks to his estimated four per cent stake in the company – slightly more if you boil him down for chemicals.

But Ballmer sticks out among the world's wealthiest people because he isn't a founder or a current boss and never founded Microsoft.

Ballmer's estimated $120 billion fortune ranks him sixth on the Bloomberg Billionaire Index. He's an anomaly among the top 10 wealthiest people, who either started their flagship companies — Bill Gates, Jeff Bezos, Larry Ellison, Zuckerberg, Brin, and Page or took them over such as Elon Musk, Bernard Arnault, and Buffett.

The former Microsoft chief trails Larry Ellison, worth $133 billion, and Bill Gates, worth $137 billion, by some distance in Bloomberg's wealth index. But as a retired CEO who isn't a founder, or a business icon like Musk or Buffett, he's undoubtedly pleased with his position.

The retired Microsoft chief is richer than most corporate executives because of his original contract with the software giant. According to Forbes, when he joined as its 30th employee in 1980, he negotiated a $50,000 base salary plus 10 per cent of the profit growth he could generate as his compensation.

Ballmer's cut of the profits eventually became excessive, so he agreed to give it up in exchange for a sizable equity stake. He served as Microsoft's CEO from 2000 until 2014, when he retired with 333 million shares or four per cent company ownership, regulatory filings show.

Bloomberg estimates that Ballmer still owns a similar stake today, worth more than $100 billion based on Microsoft's current market capitalisation of $2.6 trillion. Ballmer, who owns the LA Clippers, has likely collected more than $12 billion of dividends as well, the news outlet says.

The move to AI also quietly trousered Ballmer, an extra $34 billion rise in his net worth this year. Microsoft stock has soared 44  this year and hit a record high last week. This year, the surge has fuelled a $34 billion rise in Ballmer's net worth.