SAN JOSE, Calif. – Steve Jobs has resigned as CEO at Apple, the company he co-founded at age 21 and turned into an international business icon, known for its tremendous profits and elegantly designed devices like the iPhone, iPad and Mac computers.

The Cupertino, Calif., company announced Wednesday that veteran executive Tim Cook has been named as Jobs’ replacement.

In a letter released Wednesday afternoon, Jobs said the time to leave had arrived.

“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,” Jobs wrote, in a letter addressed “to the Apple Board of Directors and the Apple Community.”

Apple offered no further detail on why Jobs was stepping down. The 56-year-old Jobs has been on his third medical leave after previously being treated for pancreatic cancer and a liver transplant.

The company said the board had voted to elect Jobs as chairman. In his letter, Jobs told the Apple board, “I would like to serve, if the Board sees fit, as Chairman of the Board, director and Apple employee.” He also recommended the company implement its succession plan by naming Cook as CEO.

“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,” Jobs added. “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 letter was signed, simply, “Steve.”

In a statement released by the company, Apple director Art Levinson praised Jobs for his iconic role at the company.

“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 Levinson, who is also chairman of Genentech.

“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.”

Levinson added that the board “has complete confidence that Tim is the right person to be our next CEO. 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.”

Cook, who had been acting in Jobs’ place while Jobs was on medical leave, had previously served as chief operating officer, responsible for the company’s worldwide sales, supply chain and other operations.

The 50-year-old Cook had previously stepped in for Jobs in 2004 and 2009..

Apple’s stock dropped more than 5 percent in after-hours trading Wednesday after the company released Jobs’ letter.