Apple issued a surprise announcement Mondaythat Scott Forstall, the head of its mobile operating system , will be leaving next year. The company also announced that retail head John Browett will leave immediately.

Forstall has been at Apple for 15 years. He joined the company in 1997 when Apple acquired NeXT Computer in order to rehire the late Steve Jobs, and has often been singled out as the executive most like the company’s late founder. He is credited with being one of the original architects of the Mac’s operating system, Mac OS X, and being the driving force behind much of the company’s user interface designs.

Forstall’s ouster comes after lukewarm reactions to two of his most visible projects — Siri and Apple Maps. Siri, while considered a cool feature with potential, has been in “beta” testing since its launch last year.

Uproar over Apple’s new maps program, which replaced Google’s more popular and comprehensive application on the iPhone, led to a public apology from Apple chief executive Tim Cook over the poor quality of the application.

According to reports from the Wall Street Journal and the New York Times, Forstall also was let go partially because he refused to sign that apology letter.

He also was reportedly in conflict with design lead Jony Ive — another favorite of Jobs’ — to the extent that the two wouldn’t sit in the same room together. In the New York Times, an unnamed Apple employee said that news of Forstall’s departure was “better than the Giants winning the World Series.”

This is the most significant staffing change that Cook has made since taking over the company last August. The move also elevates the positions of four important Apple executives. Ive is now the head of a “human interface” group; engineering head Bob Mansfield will lead a cross-company wireless team; iTunes and iAd lead Eddy Cue will take over Siri and Mapad and Craig Federighi, who had been head of software engineering for the Mac, will take on the additional responsibilities for the mobile operating system, iOS.

The move signals a couple of things about the company’s strategy. For one, iOS and OSX may be even more integrated than they were before, now that both are under Federighi. Second, the decision to put Ive in charge of all “human interface” decisions indicates that Apple may bring the minimalist threads of its hardware design into iOS itself.

Specifically, Ive is said to dislike the “skeumorphic” designs in iOS that make the software look like real world objects — for example, the leather stitching design on the company’s calendar program or the double-reel design on its Podcasts app.

The announcement does explain some puzzles at Apple, most notably the brief retirement of Apple veteran Mansfield, who announced his retirement in June and returned in August.

The end of Browett’s time at Apple is less surprising. The executive, who has been at the company for less than year, landed himself in trouble when he began cutting staff at its stores. His changes were quickly reversed and Apple issued a statement that the decision was “a mistake” that compromised its commitment to customer service.

Until Apple finds a replacement, the retail section of the company will report directly to Cook. Forstall will stay on at the company as an “adviser” to Cook, but the release said he will leave the company next year.

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