Steve Ballmer is now worth $158 billion — more than his former Microsoft boss Bill Gates

• Bill Gates' former assistant is now wealthier than him for the first time.
• Steve Ballmer, who succeeded Gates as Microsoft CEO, is worth about $158 billion.
• Microsoft stock has surged amid a broader AI boom, boosting Ballmer's net worth.

A former assistant to Bill Gates has scaled the ranks of the world's wealthiest people to become richer than his old boss for the first time.

Steve Ballmer's fortune has more than doubled from $77 billion in November 2022 to $158 billion at Tuesday's close, putting him sixth on the Bloomberg Billionaires Index .

Gates, Microsoft's legendary cofounder and perhaps the world's best-known philanthropist , is in seventh place and worth $157 billion. He was $17 billion richer than Ballmer a year ago.

Ballmer is now about $6 billion behind Alphabet's cofounder Larry Page, who is in fifth place on Bloomberg's list at $164 billion.

Ballmer, the owner of the Los Angeles Clippers basketball team, ranks above the likes of Oracle's Larry Ellison ($157 billion), Alphabet's Sergey Brin ($154 billion), Warren Buffett ($129 billion), Reliance Industries' Mukesh Ambani ($118 billion), Michael Dell ($117 billion), and Nvidia CEO Jensen Huang ($108 billion).

Ballmer owes his wealth to joining Microsoft in 1980 as an assistant to the president — a role more akin to a business manager than a PA. He originally agreed to a $50,000 base salary plus 10% of the profit growth he generated. But Ballmer's compensation soon became outsize, so he agreed to exchange it for a significant equity stake, Forbes reported .

A close advisor to Gates, he succeeded him as CEO in 2000. Ballmer stepped down in 2014 with 333 million shares, or a 4% stake, regulatory filings show .

Bloomberg's estimate of Ballmer's wealth assumes that he's retained most of his Microsoft shares. The outlet values his stake at more than $150 billion based on Monday's $459 closing price — over nine times its split-adjusted level in 2014 when Ballmer left. He's likely to have collected dividends worth billions of dollars over the years as well.

Ballmer's net worth has skyrocketed over the past 18 months because of the artificial-intelligence boom, which Microsoft has tapped into by investing in the industry star OpenAI. The stock's price has jumped by over one-third in the past year alone.

Gates has fallen behind Ballmer because he's diversified his personal investment portfolio away from Microsoft stock and made large donations to his foundation and other charities.

Even so, it's striking that Ballmer is officially richer than Gates, given how rare it is for an employee to become wealthier than his company's founder.