“I would lean toward an optimistic view,” said Michael Maccoby, a management consultant and author of the book “The Productive Narcissist: The Promise and Peril of Visionary Leadership.” “Steve Jobs is a hard act to follow but not an impossible one. I see so many positive factors here. Apple has created a platform, a technology, patents, processes. It’s created the Apple stores. It’s created attitudes among customers.”

Still, genius on the Jobs level is not exactly plentiful.

“Steve could build something beautiful and take all of the fright out of it. What the early Macs did was say a computer is just a tool, anyone can use it,” said Jay Elliot, an early Apple executive.

“He’s leaving Apple with a long-term vision that his successors will implement,” said Mr. Elliot, who has written a book on Mr. Jobs’s leadership style. “But in three or five years they’re going to have to find some other visionaries.”

Investors seem not to be looking that far ahead. Apple’s stock, which slid in after-hours trading Wednesday when the news was first released, fell only modestly Thursday even as the overall market stumbled, closing down 0.7 percent, at $373.72. They may be drawing comfort from the fact that Mr. Jobs is still around as chairman. He was on the Apple campus Wednesday for a board meeting, according to a person with knowledge of his whereabouts.

Mr. Cook, with his soft-spoken demeanor, is at an advantage because his personality is the opposite of Mr. Jobs’s, who was mercurial, said Jeffrey Pfeffer, a professor of organizational behavior at Stanford. They would otherwise be compared, and Mr. Cook would inevitably be described as “Steve Light.”

“It’s better to be different than a second-rate version of what the last person was,” Mr. Pfeffer said. He compared the situation to that of Southwest Airlines, whose colorful co-founder, Herbert D. Kelleher, eventually stepped down and was replaced by a more sedate executive, Gary C. Kelly.