net worth: $4.5 billion
elizabeth holmes is the youngest female billionaire in the world thanks to the success of her pain- and needle-free blood-testing company theranos. when she was 19, holmes dropped out of stanford to found the company and has dedicated her life to it. according to a 2014 new yorker profile, the ceo lives in a "two-bedroom condo in palo alto...no longer devotes time to novels or friends, doesn't date, doesn't own a television, and hasn't taken a vacation in ten years."
though holmes' image is that of a well-intentioned hard worker, she's facing harsh criticism for reports claiming dodgy business practices. "this is what happens when you work to change things," holmes fired back. "first they think you're crazy, then they fight you, then you change the world."