Steven P. Jobs, co-founder and leading product visionary, has stepped down at Apple.  would step down as chief executive.  He now will be replaced by Tim Cook, the chief operating officer. 

In a letter to Apple’s board of directors and “the Apple community,” Mr. Jobs said he'd like to remain as chairman, saying:  “I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple’s C.E.O., I would be the first to let you know.  Unfortunately, that day has come.”

Mr. Jobs, 56, had surgery for pancreatic cancer in 2004 and had a liver transplant in early 2009.  His health has gone through considerable ups and downs in recent years, according to a person briefed on his condition.

Although he has officially been on medical leave since January, Mr. Jobs has appeared in public to announce new Apple products. In June he was on stage in San Francisco to talk about iCloud, Apple’s latest foray into cloud-based computing. It is not clear how much Mr. Jobs has been involved in the company’s day-to-day operations recently. Apple is expected to unveil a new model of its hugely successful iPhone this fall.

“I believe Apple’s brightest and most innovative days are ahead of it. And I look forward to watching and contributing to its success in a new role,” Mr. Jobs said in the letter.

Reaction to the Announcement.   Apple’s stock dropped in after-hours trading, falling nearly 5%. Michael Gartenberg, research director at Gartner, said that although this marks the end of an era for Apple, Mr. Jobs should still be able to shape Apple’s products in the chairman role. Further, “it’s important to remember that there’s more to Apple than any one person, even Steve Jobs.”

What Steve Jobs Accomplished at Apple.   Mr. Jobs founded Apple in 1976 with Steve Wozniak, and built the company’s reputation with the Apple II and Macintosh computers.  He left Apple in 1985 after a conflict with then CEO John Sculley.  The following year, with a small group of Apple employees, he founded NeXt Computer, which ultimately focused on the corporate computing market, without notable success.  In 1986, he bought the computer graphics division of Lucasfilm and re-established it as the independent animation studio Pixar.

A decade later he sold the NeXt operating system to Apple and returned to the company.  In short order he was again at the helm and set out to modernize the company’s computers.

With the more recent introduction of the iPod, iTunes, iPhone and iPad, Apple has shaken up a range of industries. Mr. Jobs has been awarded much of the credit for turning Apple into one of the world’s most valuable companies.  Last month Apple briefly became the most valuable company in the world in terms of market capitalization.

“In his new role as chairman of the board, Steve will continue to serve Apple with his unique insights, creativity and inspiration,” said Art Levinson, the chairman of Genentech and an Apple board member, in the company’s announcement.

Mr. Cook has been Apple’s acting CEO since Mr. Jobs went on medical leave.  Before joining Apple, he was VP for corporate materials for Compaq.   [NYTimes, 8/24/11]