After his announcement, Apple stock quickly fell 5.4 percent in after-hours trading.
The company said Jobs gave the board his resignation and suggested Cook be named the company's new leader. Apple said Jobs was elected board chairman and Cook is becoming a member of its board.
Jobs' hits seemed to grow bigger as the years went on: After the colorful iMac computer and the now-ubiquitous iPod, the iPhone redefined the category of smart phones and the iPad all but created the market for tablet computers.
His own aura seemed part of the attraction.
On stage at trade shows and company events in his uniform of jeans, sneakers and black mock-turtlenecks, he'd entrance audiences with new devices, new colors, new software features, building up to a gran finale he'd predictably preface by saying, "One more thing.''
Jobs, 56, shepherded Apple from a two-man startup to Silicon Valley darling when the Apple II, the first computer for regular people to really catch on, sent IBM Corp. and others scrambling to get their own PCs to market.
After Apple suffered slump in the mid-1980s, he was forced out of the company. He was CEO at Next, another computer company, and Pixar, the computer-animation company that produced "Toy Story'' on his watch, during the 10 years before he returned.
The January leave was Jobs' third medical leave over several years. He had previously survived pancreatic cancer and received a liver transplant.
A press release issued by the company says:
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."
The 56-year-old cancer survivor presented Apple's new operating system, dubbed "Lion", at a developers conference.
He went on leave in January, his third medical absence since 2004, but retained his title of chief executive at Apple.
Jobs underwent an operation for pancreatic cancer in 2004 and received a liver transplant in 2009.
Appleinsider.com has just published this statement from the Apple board:
"Steve's extraordinary vision and leadership saved Apple and guided it to its position as the world's most innovative and valuable technology company," said Art Levinson, Chairman of Genentech, on behalf of Apple's Board. "Steve has made countless contributions to Apple's success, and he has attracted and inspired Apple's immensely creative employees and world class executive team. In his new role as Chairman of the Board, Steve will continue to serve Apple with his unique insights, creativity and inspiration."
He also recommended that Cook, who has fulfilled Jobs' duties as CEO during his medical leave, take over as the chief executive. The board also agreed with Jobs' assessment, and Cook is now CEO.
"The board has complete confidence that Tim is the right person to be our next CEO," Levinson said. "Tim's 13 years of service to Apple have been marked by outstanding performance, and he has demonstrated remarkable talent and sound judgment in everything he does."
Tim Cook has had to step in for his boss at least three times in recent years. A Silicon Valley veteran, who worked at IBM and Compaq before joining Apple in 1998, Cook is well known to Wall Street analysts, and well respected for his command of the minutiae of Apple's manufacturing business and his ability to squeeze efficiencies in the production of its products.
Earlier this month Apple became the most valuable listed company in the United States, surpassing Exxon Mobil .
Gleacher & Co. analyst Brian Marshall said at the time that Apple was giving investors something that has never been seen before. Apple's numbers are huge, with $US30 billion in revenue in the latest quarter, for example. Yet Marshall said the 35-year-old company is "growing like a startup."
"Even in 2008 and 2009 Apple grew like a weed and the world was coming to an end," Marshall said.
Apple grew its net income 70 per cent to $14 billion and its revenue 52 per cent to $65 billion in the fiscal year that ended last September. A year earlier, even as other companies were reeling from the economic meltdown, Apple's earnings grew 35 per cent and its revenue 14 per cent.
Apple wasn't always a tech darling. The company once known as Apple Computer Inc. was on a steep decline before Jobs returned in 1997.
With Jobs as CEO, Apple dreamed up gadgets that people didn't even think they needed until they got their hands on them or saw friends and relatives with them.
There were music players, smartphones and tablet computers before Apple introduced the iPod, the iPhone and the iPad. But the Apple gadgets' sleek, minimalist design and intuitive software gave them a loyal following not just by tech geeks but the everyday consumers.
"Never underestimate the power of Joe Sixpack relative to expenditures on consumer electronics," Marshall said.
People want their gadgets, especially those made by Apple, even in a recession and even as they watch their stock portfolios and retirement funds shrink.
Even so, Apple commands just a sliver of the overall smartphone and computer market. For that reason, Apple can grow at such a fast pace. "They have just a tremendous runway in front of them," Marshall said.
Apple's growth is limited only by innovation. Investors expect it to grow as long as it keeps making products that people want. So investors are betting on Apple's stock even though it currently makes less money than Exxon.
In its latest quarterly report, Apple said stronger iPhone and iPad sales helped more than double its net income to $7.3 billion and grow revenue by 82 per cent to $29 billion.
Apple generally introduces a new product every three years, which means something new in 2013. Marshall does not expect the company to slow down any time soon.
In fact, he expects Apple to pass yet another milestone next year, when it's likely to surpass Hewlett-Packard Co. as the world's largest technology company by revenue. In the most recent quarter, HP reported $31.6 billion in revenue, compared with Apple's $28.6 billion in its latest quarter.
- NZ HERALD ONLINE / AP / AFP