Bill Gates' former assistant is the world's 5th-richest person - and he's close to overtaking the Microsoft cofounder

• Bill Gates' ex-assistant could soon overtake the Microsoft cofounder and his former boss in wealth.
• Steve Ballmer's estimated $115 billion fortune puts him just behind Gates on Bloomberg's rich list.
• Ballmer owes his vast wealth to the contract he negotiated when he first joined Microsoft in 1980.

Bill Gates' ex-assistant has rocketed up the list of the world's richest people, and could soon overtake Microsoft's world-famous cofounder and his former boss in net worth.