Brian Valentine, who herded the past three versions of Microsoft's flagship operating-system software toward completion, left the company Friday to take a senior position at Amazon.com.

Called upon by CEO Steve Ballmer in the late 1990s to drive struggling Windows 2000 over the finish line, Valentine's departure coincides with the release of a near-final version of Vista, which also has been plagued by delays.

Analysts viewed the senior vice president's exit as part of a regular cycle that tends to coincide with the completion of Microsoft's major products, and as a sign that Vista is on track to meet its schedule.

"It wouldn't be unusual to see some fall-off of the people associated with a big project like Windows Vista," said Dwight Davis, a software-industry analyst at Ovum Summit. "I doubt that Brian would have left if there were a lot of major problems still associated with the [Vista] code."

After 19 years at Microsoft, Valentine will join Amazon as a senior vice president in mid-September, said Patty Smith, a company spokeswoman. She would not say what role he will play at the Seattle-based Internet retailer.

"We're delighted to have him," Smith said. "... We don't normally comment on executive arrivals."

Valentine, whose formal title was senior vice president of the Windows Core Operating System Division, appears to be leaving Microsoft on good terms.

"Brian played a critical leadership role and his contribution to the success of many Microsoft products is significant and indelible," a company representative said in an e-mail Tuesday. "Microsoft wishes him well on his next challenge outside the company."

The 46-year-old Centralia native and graduate of Eastern Washington University was not made available for an interview by Microsoft and could not be reached.

Though Amazon isn't disclosing Valentine's job, executives tend to define their roles, at least in part, themselves.

"Somebody like Brian doesn't have to post his résumé on Monster.com," said Laura DiDio, Yankee Group analyst. "I'm sure that Amazon is giving him a lot of latitude."

One area where he could focus is Amazon's emerging digital-media effort.

Since the start of 2003 Amazon has invested $1.3 billion in technology and content with no big prize to show for it.

A blogger caused a stir recently by posting unconfirmed screen shots of Amazon Unbox, software that would allow consumers to purchase, download and play digital movies.

While Amazon never comments on future projects, the company registered the word "Unbox" with the U.S. Patent and Trademark Office in mid-August.

In its filing, Amazon said Unbox would be used to sell goods and services, namely "downloadable computer software for the delivery and viewing of digital media."

Valentine brings to Amazon the respect of software engineers; strong leadership abilities (including a Ballmeresque ability to rally the troops); and a sense of humor, once masquerading as John Belushi's Bluto Blutarski in a Microsoft video spoof of "National Lampoon's Animal House."

After the Windows 2000 effort, Valentine and others said that they would get Windows out on a regular schedule and revise the difficult and unpredictable development process, said Rob Helm, an analyst with Directions on Microsoft.

As Vista comes to its conclusion — now more than two years late — "it was by every measure as difficult a development cycle" as Windows 2000, Helm said.

Valentine bears some responsibility for the Vista delays, but "you could argue that the project itself was overly ambitious and I don't know if anybody in his role could have done a better job of getting the operating system out on time," said Davis at Ovum Summit.

While Valentine walks out the door with a lot of institutional knowledge, it's not irreplaceable and new leaders are already stepping into the Windows Division, Helm said.

Valentine reported to division Co-Presidents Kevin Johnson and Jim Allchin, who is planning to retire at year's end. Jon DeVaan now takes full control of the Core Operating System Division.

He's shared the job with Valentine since early last month, when Microsoft said Valentine and two other senior executives would be moving to other positions within the company on completion of Vista.

DeVaan was previously working with Chairman Bill Gates on better ways of building large software systems.

Heading the Windows and Windows Live group is Steven Sinofsky, who amassed an on-time record as senior vice president in the division that builds Microsoft's other major product: Office.

"The leadership at Windows is changing bottom up," Helm said. "There isn't going to be a void. There's going to be a whole new order."

Benjamin J. Romano: 206-464-2149 or bromano@seattletimes.com. Seattle Times business reporters Monica Soto Ouchi and Kim Peterson contributed to this report.