By all accounts, Mr. Jobs's perfectionism, autocratic managerial style and disregard for conventional wisdom are at the heart of Apple's remarkable streak of success.
Since he returned to Apple in 1996, the company has set a new standard for design in personal computers, built a chain of sleek and always-crowded stores, jump-started the sale of digital music and turned the mobile phone into a fun, flexible computer.
This is clearly the stuff of business legend. But now the company faces the real possibility that its inspirational leader may fade from the scene. Mr. Jobs, Apple's co-founder and chief executive, said on Wednesday that he was taking a leave of absence from Apple until June because his health issues -- he is a survivor of pancreatic cancer -- are "more complicated" than he first thought.
That terse letter, after he had played down his illness just last week, left Apple watchers asking what might happen to the company if Mr. Jobs does not return in June as planned.
Analysts are quick to point out the strength of the company's management bench. Timothy D. Cook, its longtime chief operating officer, will take over at least temporarily and is responsible for Apple’s manufacturing and sales operation, which are the envy of the consumer electronics industry. Jonathan Ive, Apple’s design chief, runs the team that has created much of the functional, visceral and emotional allure of Apple products, whose design ambitions extend right down to its elegant packaging.
But some Apple watchers and former employees are skeptical about Apple's fate if it is forced to soldier on without Mr. Jobs. "If you look at the history, Apple can coast for several years and still do very well," said Paul Mercer, who worked for Apple in the 80s and subsequently developed software that was used to design the user interface for the first iPod. "But it's very risky, and without Steve, the long term is untenable."
The stories about Mr. Jobs are well known, like his insistence that even the insides of the Macintosh computer, which hardly anyone ever sees, should look good. His obsession with detail permeates everything Apple does, and that principle will certainly not disappear from the company if he is gone.
But there are other aspects of his role that do not get as much attention and may be more difficult to replace. At many technology companies, various divisions often work at cross purposes, competing with one other to develop related products. This can lead to devices and software that are sometimes incompatible, frustrating customers. Mr. Jobs, former Apple employees say, has the authority and long-term vision to yoke Apple managers and employees together under a single cause.
"Steve is terrific at attracting and retaining people, creating an agenda and getting people to stick to it," said Stephen G. Perlman, a Silicon Valley entrepreneur who was a principal scientist at Apple in the 1980s. "It's very hard to find somebody who is so credible, and who has such a strong following that he is able to cut through corporate politics."
Mr. Jobs has also been Apple's chief deal maker. After introducing the iTunes store in 2003, he persuaded entertainment companies to sell digital versions of their products when they were largely bivouacked, hiding in fear of piracy. In large part because of Mr. Jobs's efforts, those barriers have fallen, though other challenges remain like getting the Hollywood studios to relax their restrictions on renting or downloading movies over the Internet.
In their moments of great anxiety, Apple fans look back to the late '80s and early '90s for a glimpse of Apple without Mr. Jobs. After he was ousted in a boardroom coup in 1985, Apple actually thrived for several years, unveiling the first Mac with a color screen, the PowerBook laptop and QuickTime, which broke ground in bringing video to personal computers.
But then, to the horror of its diehard fans, Apple withered. Its stock fell 68 percent from its 1991 peak to Mr. Jobs's triumphant return in 1996.
In the meantime, three chief executives came and went, and Apple’s core product, the Macintosh, did not evolve as fast as computers based on Microsoft Windows.
Part of the problem, say people who were at Apple during the lean years, could be traced back to Mr. Jobs himself: he had not allowed anyone with talents similar to his own to rise at the company. Some think that may also be true today.