When Steve Ballmer was 24 years old, he dropped out of Stanford University’s business school to join his former Harvard classmate Bill Gates at Gates' tech start-up Microsoft. Although it unnerved his parents, the decision allowed Ballmer to work for one of the fastest growing companies in the country and go from Gates' assistant to the company’s CEO.

Today, he’s one of the richest people in America, with an estimated net worth of $40.7 billion. Here's how he made it happen.