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.

A graduate of Auburn with an M.B.A from Duke University's Fuqua business school, Cook has largely shunned the limelight, leaving the keynotes and column inches to his larger-than-life CEO.

This, however, does not mean that the Alabama native's abilities should be under-estimated, according to those who knew him earlier in his career.

" Tim Cook was considered a leader, and he was a really, really good student -- well-liked by his peers, always prepared, tough, but fair," said Blair Sheppard, dean of Duke University's school of business, in an email Thursday. "We would have predicted great things for him, though it would have been difficult to predict he'd head one of the world's most iconic brands."

More recently, as Apple's COO, Cook headed the firm's crucial Mac division and was responsible for the company's worldwide sales and operations, so he knows a thing or two about Apple's all-important brand.

Cook, who has worked at Compaq and Intelligent Electronics, also spent 12 years at IBM ( IBM), where he led manufacturing and distribution for the company's PC business in North and Latin America.

"Cook is kind of the steady hand at the tiller," says Ezra Gottheil, an analyst at Technology Business Research (TBR), explaining that he already has experience of running Apple. "His executive career has been excellent -- he stepped in when Jobs was out of the picture for a while in terms of his cancer."

The COO did indeed take the company's reins for two months in 2004 when Jobs was receiving treatment for pancreatic cancer, fading into the background when his CEO returned.

But Gottheil acknowledges that Apple could still feel the impact of Jobs' absence, even with Cook at the helm. Jobs, he explains, has a gift for understanding exactly what consumers want from electronic devices, and quickly translating this into products.

"If Jobs is not coming back, Apple might not have the consistent ability to take these innovative leaps into new businesses and new product lines," he warns.

Cook will certainly have his hands full during the coming months. In addition to reassuring investors that the firm's product roadmap will be unaffected by Jobs' absence, he must also deal with the consumer spending slowdown.

With a number of analysts predicting weakening demand for iPhones, iPods, and Macs, Cook must keep Apple's products, as opposed to its management changes, in the public eye.

Apple, of course, is notoriously secretive about its product plans, and there has also been speculation that lawsuits could fly in the aftermath of Jobs' departure.

Attention is already focused on Apple's recent disclosures on Steve Jobs' health, and opportunistic lawyers will be closely monitoring the firm's share price, according to John Coffee, professor of law at Columbia University.

"Lawsuits are a product of how large or how sudden the stock market drop is," he says. "The plaintiff's bar is very entrepreneurial - but the fact that the lawsuit is brought doesn't mean that there will be liability imposed or that Apple made materially false statements."

Apple's many rivals, which include Nokia, Palm, Research In Motion, Hewlett-Packard and Dell, will also be following Cook's every move, and will be quick to exploit any slip-ups.

Apple shares slipped $2.28, or 2.67%, to $83.06 Thursday, as the Nasdaq rose 1.49%.