He may be a college drop-out and "computer geek" but rivals have often underestimated his abilities in the cut throat world of business.
Despite the wealth and ruthless domination of the global computer industry, Gates maintains it is the programming itself which is his abiding passion.
He stood down as chief executive of Microsoft in 2000, to focus on software development and the new challenges of the mobile internet age.
The one-time high school computer enthusiast - whose worth passed the $100bn mark in 1999 - said he wanted to immerse himself again in the work he loves most.
Gates has come to be known for his aggressive business tactics and confrontational style of management.
He, and his company, have attracted a vast army of critics and enemies in recent years as their domination of the IT world has grown.
He was born on 28 October, 1955, growing up with two sisters in Seattle. Their father, William H. Gates II, is a Seattle attorney, and their late mother, Mary Gates, was a schoolteacher.
Gates began computing as a 13-year-old at the city's Lakeside school.
By the age of 17, he had sold his first program - a timetabling system for the school, earning him $4,200.
It was at Lakeside that he met fellow student Paul Allen, who shared his fascination with computers.
During Gates' stint at Harvard, the two teamed up to write the first computer language program written for a personal computer.
The PC's maker, MITS, liked their work and the two friends established Microsoft in 1975, so-called because it provided microcomputer software.
A year later, Gates dropped out of Harvard, once it became clear that the possibilities for Microsoft were bright.
The big break came in 1980 when an agreement was signed to provide the operating system that became known as MS-DOS, for IBM's new personal computer.
In a contractual masterstroke, Microsoft was allowed to licence the operating system to other manufacturers, spawning an industry of "IBM-compatible" personal computers which depended on Microsoft's operating system.
That fuelled further growth, prompting the company to float in 1986, raising $61m.
Now a multi-millionaire, Allen had already stepped back from the frontline. But Gates continued to play the key role in the company's growth, with his vision for networked computers proving central to Microsoft's success.
However, his judgement has not always appeared flawless.
While sales and profits rocketed in the early 1990s, he was seen to have misjudged on a grand scale the possibilities and growth of the internet.
Outside of Microsoft he also has interests in biotech companies, sitting on the board of the Icos Corporation and has a stake in Darwin Molecular, a subsidiary of British-based Chiroscience.
He founded Corbis Corporation, which is developing a digital archive of art and photography from public and private collections around the globe.
His books, The Road Ahead and Business @ the Speed of Thought have both hit the best seller lists.
Gates married Melinda on New Year's Day 1994.Together they have three children - Jennifer Katharine, born in 1996, Rory John, born in 1999, and Phoebe Adele, born in 2002
He met his wife in 1987 at a Microsoft press event in Manhattan. She was working for the company and later became one of the executives in charge of interactive content.
Other interests listed on his official website are reading and playing golf and bridge.
Gates and Melinda have been giving increasing amounts of money to charity, with his father running a foundation.
It has been endowed with billions to support initiatives in the areas of global health and education.
It is the world's second richest philanthropic organisation, and within shouting distance of the world number one, The Wellcome Trust in the UK.