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 today from the company he and childhood friend Paul Allen started in a garage in 1975.

He eases into retirement ranked third richest person in the world behind US investor Warren Buffet and Mexican tycoon Carlos Slim. Although he jokes publicly that he will 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. He fell in love with the machines and school officials tapped into his programming prowess, swapping computer time for his services.

Gates met Steve Ballmer, now Microsoft’s chief executive, while the two were students at Harvard University. Gates 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. In the early years at Microsoft, Gates reviewed every line of computer code written.

His fascination with technology remains unabated and his enthusiasm is unleashed when talks turn to the nuts-and-bolts of computer innovations.

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.