Nathan Myhrvold, Microsoft's chief technology officer of 14 years, resigned from his post last week.
The move came as no surprise, as Myhrvold had announced last year that he would be taking a sabbatical from the company.
Myhrvold joined Microsoft in 1986 when the company bought Dynamical Systems Research, a company he founded with his brother, Cameron. He will continue as a consultant to Microsoft's chairman Bill Gates, company sources said.
"Nathan's contributions to Microsoft and to the creation of Microsoft Research were critical," Gates said.
"I look forward to continuing to work with Nathan, although it won't be in a full-time capacity."
Myhrvold started work on Microsoft Research in 1991. "Nothing lasts forever, no matter how great it has been," Myhrvold wrote in a message to his staff.
Myhrvold, who has a close relationship with Gates, denied speculation that he was pushed out by Steve Ballmer, Microsoft's chief executive. He added that he was not leaving Microsoft to work for another company.
Myhrvold "will be focusing on other interests, including biotechnology, paleontology and philanthropy", Microsoft said in a statement.
Meanwhile, the company has promoted Rick Rashid from vice-president to senior vice-president of Microsoft Research and promoted Dan Ling from director of operations at Microsoft Research to vice- president of the group. However, Microsoft has not yet named a replacement for the chief technology officer post.
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