After seeing Windows 8 through development, Microsoft’s Steven Sinofsky is moving on from the company.

Sinofsky made his mark at Microsoft as the head of the Windows and Windows Live division, overseeing the operating system during its most radical shift in years. He often opened Microsoft events, taking the stage to introduce the system he shepherded to release as well as the company’s tablet computer, the Surface.

He took over the Windows division in 2006, after the company released the much-panned Windows Vista. After seeing much better success with Windows 7 in 2009, he followed that with the release of Windows 8 — a system completely redesigned for use with touchscreens — in October.

Driven and talented, Sinofsky was often said to be a divisive figure within the company.

According to All Things Digital, his clashes with other senior executives may have hastened his exit, though Microsoft’s release announcing the decision frames the move as a mutual decision.

“I am grateful for the many years of work that Steven has contributed to the company,” Microsoft chief executive Steve Ballmer said in a company release. “The products and services we have delivered to the market in the past few months mark the launch of a new era at Microsoft.”

“It is impossible to count the blessings I have received over my years at Microsoft. I am humbled by the professionalism and generosity of everyone I have had the good fortune to work with at this awesome company,” Sinofsky said.

Sinofsky’s duties on software and hardware engineering will be picked up by Julie Larson-Green, who has become a more common sight in recent Microsoft presentations. The business of Windows will become the responsibility of Tami Reller, who will also remain the company’s chief financial officer and chief marketing officer.

Sinofsky’s departure surprised some, particularly those who had circulated his name as a possible replacement for Ballmer down the line. But CNET’s Jay Greene reported signs of the executive’s departure were clear for those who were looking. Despite Sinofsky’s talents and intelligence, Green says his reputation for butting heads may not have worked at a company that moving quickly to weave all of its separate units to work together. Microsoft Surface is the clearest example of this, requiring hardware, software, Office, Xbox, Bing, Skype and other teams to work together closely.

Having seen Windows 8 out the door along with the Surface, it may have simply seemed to Sinofsky like a good time to leave. That, at least, is the insinuation in an e-mail Mashable obtained that’s reportedly from Sinofsky to his staff.

“Some might notice a bit of chatter speculating about this decision or timing,” the e-mail reads. “I can assure you that none could be true as this was a personal and private choice that in no way reflects any speculation or theories one might read—about me, opportunity, the company or its leadership.”

At ZDNet, Mary Jo Foley noted that Microsoft hinted at a reorganization in its most-recent proxy statement. She also said she thinks that it’s too soon to cite poor reaction to the release of Windows 8 or the Surface — which Ballmer said had seen modest sales so far — as a reason for Sinofsky’s departure.