It's all change at Apple ( AAPL): Steve Jobs' medical leave, announced yesterday, has thrust the firm's COO Tim Cook into the spotlight. But what can investors and the rest of the tech sector expect from Apple's interim boss?

Few companies are as synonymous with their CEO as Apple, a technology behemoth that has come to symbolize our gadget- and design-obsessed times, and that only adds to the already difficult task of competing in a flooded market in an economic downturn.

Investors will be wondering whether they can trust Cook to do what Apple needs to thrive: keep products, as opposed to its management changes, in the public eye and protect market share from rivals Nokia ( NOK), Palm ( PALM ), Research In Motion ( RIMM), Hewlett-Packard ( HPQ) and Dell ( DELL)?

Although lacking Jobs' star quality, Cook has quietly built up a reputation as a more-than-capable lieutenant since his arrival at Apple in 1998. The picture that emerges is of a detail-oriented, determined, under-stated executive.

A 2006 Wall Street Journal profile described the 48-year old as a "low-key operator," who has focused his energies on making sure the company runs smoothly behind the scenes. While the Apple-infatuated media have fixated on his boss' weight loss and recent MacWorld non-appearance, the temporary chief is considered competent and effective.

Cook is credited with helping turn Apple around by overhauling the firm's manufacturing and streamlining its operations. This effectively laid the foundations for the likes of the iPhone, providing Apple with a rock-solid infrastructure from which to launch its technology.

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