Technology visionary Steve Jobs, who co-founded Apple Inc and transformed it into the world’s most valuable technology company, has resigned as the company’s chief executive after a lengthy medical leave.

Jobs, 56, remains as Apple’s chairman. His role as chief executive would be taken over by chief operating officer Tim Cook, Apple said late yesterday.

“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,” Jobs said in his letter of resignation to the board. “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.”

steve jobs apple ceo quits 160109 03 Jobs’ ( left ) future as chief executive had long been questioned because of his poor health and frail appearance. Investors took news of his departure badly, sending Apple’s stock price down more than 6 percent in after-hours trading.

Jobs founded Apple in 1976 with Steve Wozniak and Ronald Wayne and played a key role in igniting the personal computer revolution. He was ousted from the company in 1985, sparking a decline in Apple’s fortunes that was only reversed when Jobs was lured back to the company in 1996.

Under Jobs, Apple’s share price rose from US$9 when he returned to the company to US$376 at the end of trading yesterday, after which Jobs announced his resignation.

This month, Apple for the first time overtook Exxon Mobil Corp as the world’s most valuable company although the two corporations have traded places several times since then amid severe market fluctuations.

Jobs introduced the iPod music player in 2001, laying the foundation for the 2007 iPhone and the iPad in 2009, which all became some of the most successful consumer electronic devices in history.

Jobs, who was diagnosed with pancreatic cancer in 2004 and underwent a liver transplant in 2009, took indefinite medical leave in January.

“Steve’s extraordinary vision and leadership saved Apple and guided it to its position as the world's most innovative and valuable technology company,” Art Levinson, chairman of Genentech, said 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,” Levinson said.

‘The end of an era’

Colleagues and fans immediately took to Twitter to comment on Jobs’ move. “Steve Jobs is the greatest leader our industry has ever known,” wrote Marc Benioff, chief executive of Salesforce.com. “It’s the end of an era.”

Analyst Carmi Levy said a key question was whether Jobs would continue to play an active role as Apple chairman. “Is Steve’s move him deciding to focus or is it him preparing for the end?” Levy asked.

“Don’t panic. Remain calm,” Colin Gillis, an analyst at BGC Partners said in an investment note. “This is not unexpected.”

- dpa