Bill Gates dropped out of Harvard University in 1975 to start Microsoft, the software company that would make him a billionaire by age 31.
Mary was a respected businesswoman with many responsibilities, including her membership on the board of nonprofit organization United Way of King County. There, she met the late John Opel, then-chairman of IBM, who also was a member of the United Way board. In 1980, Microsoft was a small, five-year-old firm and Mary saw an opportunity to help her son's fledgling company by speaking with Opel, according to The New York Times.
That's because for the first time in IBM's then 70-year history, the company was looking to outsource help for an endeavor the company called project "Chess." IBM wanted to hire an outside software maker to develop an operating system for its personal computer.
Microsoft was already in the running for the project, but IBM was considering many software companies, including Digital Research, one of Microsoft's competitors. With this knowledge, Mary used her connection and spoke with Opel about Microsoft, and afterward, Opel spoke to IBM executives about the company.
Luckily for Microsoft, IBM's talks with Digital Research started to flounder, and when assessing options, Opel remembered Microsoft as the company "run by Bill Gates, Mary Gates' son," according to The Seattle Times.
As a result, IBM "took a chance," The New York Times reported, and hired Microsoft for the job. (In addition to Microsoft, IBM also contracted Digital Research and SofTech Microsystems to adapt operating systems for IBM's personal computer.)
When Microsoft won the job, it didn't actually have an operating system of its own. So in 1981, the company bought QDOS, an operating system created by hardware company Seattle Computer Products, and with it developed MS-DOS, the Microsoft Disk Operating System. Microsoft licensed its MS-DOS to IBM to use as the operating system for its personal computer. (In addition to Microsoft, IBM also contracted Digital Research and SofTech Microsystems to use their operating systems for IBM's personal computer.)
Because the MS-DOS was non-exclusive to IBM, it became one of Microsoft's most profitable products ever. The operating system was not only used in all IBM computers at the time, but also became the go-to operating system for almost every personal computer on the market.
Gates was CEO at Microsoft until 2000, stepped down as chairman in 2008 and left the company's board in March to dedicate more time to his Bill & Melinda Gates Foundation. Microsoft currently has a market cap of $1.6 trillion.
This story has been updated to include information on the additional operating systems IBM used for its personal computer.