Bill Gates has built the world's largest software company and created the world's biggest personal fortune.
Gates had sold his first computer program by the age of 17
Now the co-founder of Microsoft - who will step down from his day-to-day role in 2008 - concentrates on giving most of his wealth away.
The business acumen and ruthless determination that helped make Mr Gates the most successful Harvard drop-out in history is being focused on tackling loftier issues.
Instead of software code, product development and strategic planning, his priorities will be the challenges posed by extreme poverty, a lack of education and diseases like AIDS and malaria.
Just as he helped launch the era of personal computing and internet communications, Mr Gates is applying his passion for technology, and quite a few billion dollars, to many of the developing world's most pressing social problems.
The career change began in 2000, when he stood down as chief executive of Microsoft, to focus on software development and the new challenges of the internet age.
It will end in July 2008 when Mr Gates will leave his Microsoft "day job" to concentrate on his philanthropic endeavours at the Bill & Melinda Gates Foundation.
"I believe that with great wealth comes great responsibility, a responsibility to give back to society, a responsibility to see that those resources are put to work in the best possible way to help those most in need," he said when announcing the move.
But although he won't be strolling through the corridors of Microsoft HQ as often, Mr Gates won't be cutting many ties.
He will keep the role of chairman and senior technical adviser and has pledged to maintain his position as Microsoft's biggest shareholder.
Gates became a multi-millionaire when Microsoft floated in 1986
Aside from his reputation as a highly driven, intelligent and prescient entrepreneur, Bill Gates has also 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 over the years as their domination of the IT world has developed.
He is a hate figure for many technology evangelists and small computer firms that feel they have been bulldozed by Microsoft's market dominance - which has in turn led to problems with US and European Union authorities.
Bill Gates was born on 28 October, 1955, growing up with two sisters in Seattle. Their father, William H. Gates II, was a Seattle attorney, and their late mother, Mary Gates, was a schoolteacher.
He began computing as a 13-year-old at the city's exclusive 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 company moved to Redmond, Washington from its original base in Albuquerque - a decision attributed by some to a young Mr Gates' frequent run-ins with New Mexico's traffic police.
Microsoft's first staff photo, from the Albuquerque era
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. Mr Gates continued to play the key role in the company's growth.
The development of mass market software like the Windows operating system and Office suite of word processing and spreadsheet applications meant Microsoft prospered, and so did he - his fortune briefly passing the $100bn mark in 1999.
However, his judgement has not always appeared flawless.
Although 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 - a technology platform that Microsoft has been unable to replicate its market dominance on.
He also found time to start Corbis Corporation, which is developing a digital archive of art and photography from public and private collections around the globe.
Bill Gates married Melinda French on New Year's Day 1994 and together they have three children - Jennifer, born in 1996, Rory, born in 1999, and Phoebe, born in 2002.
They live in a huge $125m house built into the side of a hill overlooking Lake Washington.
The Bill & Melinda Gates Foundation has $29bn to spend
Other interests listed on his official website are reading, playing golf and bridge.
Since 1994 the Gates' have been giving increasing amounts of time and money to charity, eventually endowing one of the world's biggest charitable foundations, which had estimated funds of about $29bn in 2005.
Forbes magazine has listed Bill Gates as the world's richest person for the last twelve years, but in an interview last year, Mr Gates said he didn't like being in such a position.
If he does as good a job giving away his fortune as he did running Microsoft, his wish may soon come true.