San Francisco, Oct 31 : Microsoft co-founder Bill Gates' ex-assistant Steve Ballmer is now ranked as the world's fifth-richest person on the Bloomberg Billionaires Index and close to surpassing his former boss in wealth. Ballmer's fortune has increased by an estimated $29 billion this year to about $115 billion, trailing Gates -- who is in fourth position with $121 billion -- by only $6 billion, compared to $17 billion three months ago, reports Insider. As per the index, Ballmer is currently wealthier than CTO of Oracle Larry Ellison ($114 billion), ace investor Warren Buffett ($111 billion), Google's co-founder Larry Page ($110 billion), founder and CEO of Meta Mark Zuckerberg ($108 billion), and Google's co-founder Sergey Brin ($105 billion). Ballmer joined Microsoft in 1980 as Microsoft co-founder's assistant, however, he was more of a business manager than a personal assistant. According to a report by Forbes, he initially negotiated a $50,000 base pay plus 10 per cent of profit growth, but when his portion of earnings became too large, he decided to swap it for a sizable equity position. The recent increase in Ballmer's fortune can be linked to the advancement of Artificial Intelligence, which has caused Microsoft's share prices to skyrocket. The company's investment in OpenAI, the maker of AI chatbot ChatGPT, has raised hopes for the company's ability to fight Alphabet, Google's owner, for dominance in internet search. As a result, Microsoft stock has risen 38 per cent in the last ten months. /IANS