Apple said on Wednesday that Steven P. Jobs, its co-founder and leading product visionary, would step down from the chief executive role. Tim Cook, the chief operating officer, will take over the position.

In a letter sent to Apple’s board of directors and “the Apple community,” Mr. Jobs said he would like to remain as chairman of the board.

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.

Apple’s stock dropped in after-hours trading, falling nearly 5 percent.

Michael Gartenberg, research director at Gartner, said in an e-mail message 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. Besides, he said, “it’s important to remember that there’s more to Apple than any one person, even Steve Jobs.”

Letter from Steve Jobs:

Aug. 24, 2011 — To the Apple Board of Directors and the Apple Community:

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.

I hereby resign as CEO of Apple. I would like to serve, if the Board sees fit, as Chairman of the Board, director and Apple employee.

As far as my successor goes, I strongly recommend that we execute our succession plan and name Tim Cook as CEO of Apple.

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.

I have made some of the best friends of my life at Apple, and I thank you all for the many years of being able to work alongside you.

Steve.

(Source: NY Times / YWN World Headquarters – NYC)