San Francisco - Bill Gates turned a childhood fascination with computer code into a Microsoft software empire that changed culture around the world.
Gates, 52, steps down officially on Friday from the company he and childhood friend Paul Allen started in a garage in 1975.
He eases into retirement ranked the third richest person in the world behind US investor Warren Buffet and Mexican tycoon Carlos Slim.
Although he jokes publicly that he'll be at a loss to fill days that for decades were devoted to Microsoft, Gates will have plenty to occupy him running the philanthropic Bill and Melinda Gates Foundation.
The foundation, funded by Gates and generous backing from Buffet, has a mandate to fight disease, reduce poverty, and improve education.
Gates was a 13-year-old student in the US state of Washington when he began programming computers.
Gates fell in love with the machines and school officials tapped into his programming prowess, swapping computer time for his services.
Key move
Among tales told is that while working on school computers Gates tinkered with programming to put him in classes made up mostly of girls.
Gates met Steve Ballmer, now Microsoft's chief executive, while the two were students at Harvard University. Gates, with the blessing of his lawyer father and teacher mom, left college after two years to start "Micro-soft" with Allen.
Gates has said in interviews that a new chip released by Intel convinced him the time was right for a software company.
The duo got the rights to computer software, modified it and rechristened it Microsoft Disk Operating System (MS-Dos).
A key move by Gates was to focus on licensing software to computer makers in numerous "partnerships" that resulted in affordable machines being available to the masses.
Microsoft software is used on about 90% of the world's computers.
Eternal geek
In the early years at Microsoft, Gates reviewed every line of computer code written.
The eternal geek's fascination with technology remains unabated and his enthusiasm is unleashed when talks turn to the nuts-and-bolts of computer innovations.
"A few years back I asked him what he thinks the world will look like in 2015," analyst Rob Enderle of Enderle Group said of Gates.
"He described it in terms of technology. While most people would describe the future in terms of their dreams or what life might be like, Bill Gates's future world was defined by network components and operating systems."
Known for button-down shirts, round eyeglasses and nerdish demeanor, Gates is not one to flaunt affluence.
He and his wife, Melinda, live in an earth-friendly "smart home" on a swath of hillside overlooking a lake near Microsoft headquarters in Redmond, Washington. The property has an estimated value of $125m.
Humorous side
The couple married on a Hawaiian island in 1994 and has three children.
Gates has drawn curious smiles by pulling up to work in a Porsche sports car with a baby seat strapped in the passenger side.
Gates has spoken publically of an affinity for fast cars that dates back to his youth and of run-ins with police that frowned on his fondness for speed.
While seemingly aloof, Gates has a humorous side.
There are photos of him prancing in a superhero costume at a company party and he made a comic "Bill's Last Day at Work" video that has gotten thousands of views on YouTube.
In the video, Gates feigns a loss of purpose that has him hounding friends such as U2 rocker Bono, actor George Clooney and comic Jon Stewart.
Devoted reader
Gates is said to be a devoted reader who paid about $31m for a collection of writings by Leonardo da Vinci. A rare copy of a Gutenberg Bible is said to be part of his collection.
Time magazine listed Gates as among the 100 people that most influenced the 20th Century. Time named Gates, his wife, and Bono together as Persons of the Year in 2005 for their humanitarian work.
Bill and Melinda Gates founded their eponymous foundation in 2000.
After leaving Microsoft, Bill Gates will remain its largest single shareholder and chairman of company's board of directors.
Analysts believe that while he won't be involved in Microsoft's daily affairs, he will have the ear of friend and chief executive Steve Ballmer.