In a critical blunder by IBM, Microsoft was allowed to license the operating system to others, spawning an industry of "IBM-compatible" machines dependent on Microsoft software.
"His legacy has to be as one of the shrewdest businessmen and technologist of the 20th century," said Michael Cusumano, a professor at the Massachusetts Institute of Technology's Sloan School of Management.
Microsoft went public in 1986 in one of the most celebrated offerings of its time. By the next year, the soaring stock made Gates, at age 31, the youngest self-made billionaire.
Overseeing Microsoft's steady growth, he became known as a bare-knuckles businessman and manager, sometimes dismissing a suggestion as "the stupidest thing I have ever heard."
Microsoft grew to dominate its industry and became the target of a landmark antitrust case, which it fought every step of the way before eventually settling with U.S. prosecutors.
Rob Helm, director of research at independent research firm Directions of Microsoft, said Gates will go down as one of the great businessmen in history like John D. Rockefellerfor better or for worse.
"He's never going to be necessarily a widely admired figure, but someone who created an activity that came to represent a chunk of the American economy."
(Reporting by Daisuke Wakabayashi. Editing by Braden Reddall and Maureen Bavdek.)