[4] He was skipped forward a year, entering Olympic High School in Bremerton, Washington, early where classmates recall his immersion in competitive chess, history, and general knowledge, on occasion competing at the state level.

In 2000, Forstall became a leading designer of the Mac's new Aqua user interface, known for its water-themed visual cues such as translucent icons and reflections, making him a rising star in the company.

[8] In 2005, when Jobs began planning the iPhone, he had a choice to either "shrink the Mac, which would be an epic feat of engineering, or enlarge the iPod".

[9] Jobs favored the former approach but pitted the Macintosh and the iPod team, led by Forstall and Tony Fadell respectively, against each other in an internal competition.

[4][11][12][13][14] Forstall received credit as he "ran the iOS mobile software team like clockwork and was widely respected for his ability to perform under pressure".

The newly introduced Maps application, completely designed in-house by Apple, was criticized for being underdeveloped, buggy and lacking in detail.

[18] In October, Apple reported third-quarter results in which revenues and profits grew less than predicted, the second quarter in a row that the company missed analysts' expectations.

Forstall's duties were divided among four other Apple executives: design SVP Jonathan Ive assumed leadership of Apple's Human Interface team, Craig Federighi became the new head of iOS software engineering, services chief Eddy Cue took over responsibilities for Maps and Siri, and Bob Mansfield (previously SVP of hardware engineering) "unretired" to oversee a new technology group.

Cook's aim since becoming CEO has been reported to be building a culture of harmony, which meant "weeding out people with disagreeable personalities—people Jobs tolerated and even held close, like Forstall,"[22] although Apple Senior Director of Engineering Michael Lopp "believes that Apple's ability to innovate came from tension and disagreement.

[19][27] The Siri intelligent personal voice assistant that Forstall introduced in September 2011 has received a mixed reception with some observers regarding it as a "flop".

According to Adam Lashinsky of Fortune, when Apple issued a formal apology for the errors in Maps, Forstall refused to sign it.

[31] In a 2012 interview, Ive, then head of hardware design only, refused to comment on the iOS user interface, "In terms of those elements you're talking about, I'm not really connected to that.

[39] On December 17, 2020, Forstall was revealed to be one of the co-creators of WordArt alongside Apple engineer Nat Brown, while interning for Microsoft in 1991.