Per a request from Jobs and the company’s succession plan, COO Tim Cook has been named the new CEO, effective immediately.

In a letter addressed to the Apple board of directors and the “Apple Community” dated Wednesday, Jobs wrote:

“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.”

Jobs, who signed the letter “Steve,” has been battling a potentially life-threatening illness on and off for several years, though he made no mention of his health in his resignation letter.

Apple board member Art Levinson confirmed that Jobs will be chairman of the board, where he “will continue to serve Apple with his unique insights, creativity and inspiration.” Jobs remains a board member at Walt Disney, a position he has held since the media conglomerate purchased Pixar in 2006.

Apple shares fell in after-market trading, shedding about 6 percent as of 7 p.m. ET