Steve Jobs, the mind behind the iPhone, iPad and other devices that turned Apple into one of the world's most powerful companies, has quit as CEO, saying he can no longer handle the job but will continue to play a leadership role.
The move appears to be the result of an unspecified medical condition for which Jobs took a leave from his post in January.
Apple's chief operating officer, Tim Cook, was quickly named CEO of the company Jobs co-founded 35 years ago in his garage.
In a letter addressed to Apple's board and the "Apple community", Jobs said he "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."
The company said Jobs gave the board his resignation yesterday 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.
Genentech chairman Art Levinson, in a statement issued on behalf of Apple's board, said Jobs' "extraordinary vision and leadership saved Apple and guided it to its position as the world's most innovative and valuable technology company".
He said that Jobs would continue to provide "his unique insights, creativity and inspiration" and that the board had "complete confidence" that Cook is the right person to replace him.
"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," Levinson said.
Jobs' health has long been a concern for Apple investors who see him as an industry oracle who seems to know what consumers want long before they do.
After his announcement, Apple stock quickly fell 5.4pc in after-hours trading.
Jeff Gamet, managing editor of The Mac Observer online news site focused on Apple, said Jobs' departure had more sentimental than practical significance, and that he had been telegraphing the change for several years.
"All Apple really has done is made official what they've been doing administratively for a while now, which is Tim runs the show and Steve gets to do his part to make sure the products come out to meet the Apple standard," he said.
"I expect that even though there are a lot of people that right now are sad or scared because Steve is stepping back from the CEO role, that ultimately they'll be okay," Gamet said.
But Trip Chowdhry, an analyst with Global Equities Research, said Jobs' maniacal attention to detail was what set Apple apart.
He said Apple's product pipeline might be secure for another few years, but predicted that the company would eventually struggle to come up with market-changing ideas. "Apple is Steve Jobs, Steve Jobs is Apple, and Steve Jobs is innovation," Chowdhry said.
"You can teach people how to be operationally efficient, you can hire consultants to tell you how to do that, but God creates innovation. Apple without Steve Jobs is nothing."
Jobs started Apple Computer with a high school friend in a Silicon Valley garage in 1976, was forced out a decade later, then returned to rescue the company.
During his second stint, Apple grew into the most valuable technology company in the world. Jobs invented and masterfully marketed ever-sleeker gadgets that transformed everyday technology, from the personal computer to the iPod and iPhone.
Cultivating Apple's counter-cultural sensibility and a minimalist design ethic, he rolled out one sensational product after another, even in the face of the late-2000s recession and his own failing health.
Jobs helped change computers from a geeky hobbyist's obsession to a necessity of modern life at work and home, and in the process he upended not just personal technology but the mobile phone and music industries.
Perhaps most influentially, he launched the iPod in 2001, which offered "1,000 songs in your pocket".
Over the next 10 years, its white earphones and thumb-dial control seemed to become as ubiquitous as the wristwatch.
In 2007 came the touch-screen iPhone, and later its miniature "apps", which made the phone a device not just for making calls but for managing money, storing photos, playing games and browsing the web.
And in 2010, Jobs introduced the iPad, a tablet-sized, all-touch computer that took off even though market analysts said no one really needed one.
Earlier this month, Apple briefly surpassed Exxon Mobil as the most valuable company in America.
Under Jobs, the company cloaked itself in secrecy to build frenzied anticipation for each of its new products.
Jobs himself had a wizardly sense of what his customers wanted, and where demand did not exist, he leveraged a cult-like following to create it.
When he spoke at Apple presentations, almost always in faded blue jeans, sneakers and a black turtleneck sweater, legions of Apple acolytes listened to every word.
He often boasted about Apple successes, then coyly added a coda -- "One more thing" -- before introducing its latest ambitious idea.
In recent years, Apple investors also watched these appearances for clues to his health.
In 2004, Jobs revealed that he had been diagnosed with -- and "cured" of -- a rare form of operable pancreatic cancer called an islet cell neuroendocrine tumour. In early 2009, it became clear he was again ill.
Jobs took a half-year medical leave of absence starting in January 2009, during which he had a liver transplant.
Last January, he announced another medical leave, his third, with no set duration. He returned to the spotlight briefly in March to personally unveil a second-generation iPad.
Jobs grew up in California and after finishing high school enrolled in Reed College in Portland, Oregon, but dropped out after a semester.
"All of my working-class parents' savings were being spent on my college tuition. After six months, I couldn't see the value in it," he said at a Stanford University commencement address in 2005. "I had no idea what I wanted to do with my life and no idea how college was going to help me figure it out."
When he returned to California in 1974, Jobs worked for video game maker Atari and attended meetings of a local computer club with Steve Wozniak, a high school friend who was a few years older.
Wozniak's homemade computer drew attention from other enthusiasts, but Jobs saw its potential far beyond the geeky hobbyists of the time.
The pair started Apple in Jobs' parents' garage two years later.
Their first creation was the Apple I -- essentially, the guts of a computer without a case, keyboard or monitor.
The Apple II, which hit the market in 1977, was their first machine for the masses.
It became so popular that Jobs was worth $100m by the age of 25.