Steve Jobs resignation as Apple CEO on Wednesday means Tim Cook, long seen as "the operations guy" at Apple, must prove he is capable of taking full charge of the company.
Cook viewed as a natural successor to Jobs has been chief operating officer, managing Apple's worldwide sales and operations, including management of its supply chain, services and support.
Perhaps more importantly, Cook has already had experience running Apple's day-to-day operations during Jobs' leaves of absence, including the period from January to the present. But there are questions about his ability to continue the spirit of innovation embodied by Jobs, whose headstrong management style inspired workers, and whose vision kept the company ahead of market trends.
"Steve Jobs has always been the visionary at Apple, and Tim Cook is the operations guy, and he's good. The problem may come in a couple of years when the company has to see things that can't be seen today," said Roger Kay, president of Endpoint Technologies Associates.
For sure, Jobs will remain at Apple as chairman, at least for now, and will be involved in design and product decisions as best he can. "Jobs will continue as chairman of [the] board, so you are talking about a guy who will continue to have influence on Apple's products ... for years to come," said Gartner analyst Michael Gartenberg.
But the state of Jobs' health is unclear, and in his letter to employees Wednesday he suggested his role will be lessened in the future. "I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple's CEO, I would be the first to let you know. Unfortunately, that day has come," he wrote in the letter.
Jobs' core strength is in seeing markets just before they happen, as he did with tablets, and he may have planned a long product pipeline for Apple to help it succeed, Kay noted. And Cook was clearly his first choice for CEO. He "strongly recommended" to the board that it appoint him to the position, he said in his letter.
Apple is in a near-unassailable position in tablets and a strong position in smartphones, and Cook would have to make big mistakes for the company to falter any time soon, which he is unlikely to do, analysts said.
There is also more to Apple than Jobs, including great design and marketing teams that have helped Apple launch its successful products, said Gartenberg. He pointed as an example to Jonathan Ive, senior vice president for industrial design, who was the creative force behind the iPhone, iPad and iPod.
As COO, Cook also headed Apple's Mac division and revamped the company's retail business by establishing its Apple stores. Prior to joining Apple in 1998, he was vice president of corporate materials at Compaq, where he managed inventory and handled material procurement.
Cook may not match Jobs in creative ability, Gartenberg said, but he is the best person to bring all the elements of Apple together.
"You need someone at the helm who is going to continue operations," he said.
(Robert McMillan in San Francisco contributed to this story.)