Microsoft is losing Ray Ozzie, the executive that many saw as having replaced Bill Gates as the software company's technical visionary.
Mr Ozzie, who joined the company in 2005, will step down as chief software architect and not be replaced in that role.
Before he goes, he will focus his efforts on the entertainment business within Microsoft, the company said in a statement yesterday.
Mr Ozzie's departure is likely to come as a shock to many Microsoft watchers given his role in shifting the company's focus to cloud computing, or web-based software that is sold on demand rather than the licensed model historically developed for Windows.
Two years ago, he introduced Microsoft's cloud computing products, an area that Microsoft has said is its future and on which it plans to spend 90pc of its annual $9bn research budget on next year.
Steve Ballmer, Microsoft's chief executive, said of Mr Ozzie that "both through inspiration and impact, he's been instrumental in our transistion toward a software world now centered on services."
When he joined the company, Mr Ozzie, 54, told executives that unless it adapted its software and the way it was sold "our business as we know it is at risk."
Mr Ozzie's decision to leave - the company didn't specifiy when - follows the departure in September of Stephen Elop, who ran the division that sells software to businesses until he left to head Nokia.
Mr Ballmer, who alongside Mr Ozzie has been the strongest proponent of the company's push into cloud computing, said that Mr Ozzie does not need replacing because the company has "strong technical leaders in each business group and strong innovation heading to market."