Bill Gates is to return to the "coal face" at Microsoft, following a major shake-up at the computer giant in which he has given up his role as chairman and Satya Nadella has been appointed chief executive.
Gates, who was 20 years old when he founded the company in 1975, will become "founder and technology adviser", and spend up to three days a week at the company "shaping strategy and product direction".
He will remain on the board but will surrender his chairmanship duties to John Thompson, the former chief executive of Symantec, and Microsoft's lead independent director.
Analysts interpreted the return of Gates, 58, to help the day-to-day running of Microsoft as his attempt to revitalise the computer business after more than a decade in the doldrums.
The company used to be the biggest technology company in the world, and for a long time enjoyed a virtual monopoly on software sales. In recent years, it has struggled to compete against mounting competition from its longstanding rival, Apple, and others such as Google and Amazon.
Microsoft's former chief executive, Steve Ballmer, made a series of attempts to turn the business around, including launching Windows phones in a tie-up with Nokia, but none of them were particularly successful. Last summer he announced plans to end his 17-year tenure.
Microsoft threw its net wide in the search for Ballmer's replacement and the third chief executive in Microsoft's history. But on Tuesday it confirmed it had opted for an insider; the Indian-born Nadella, 46, who has been with the business for more than two decades.
He pledged to tear down "obstacles" so that the company could innovate faster. He also said it was a priority to make sure employees found real meaning in their work. Mr Gates said there was "no better person" to lead Microsoft during this "time of transformation".