Steve Jobs is stepping down as chief executive at Apple, the company said on Wednesday. Jobs will remain at the company as chairman, but he and his iconic black turtleneck will be replaced by former Chief Operating Officer Tim Cook.

Jobs sent Apple a letter of resignation, which he later made public, on Wednesday. In the letter, Jobs referenced his health. He has been on medical leave from the company since January. Cook has been filling in as Apple’s CEO in Jobs’ absence. Two years ago, Jobs, 56, underwent a liver transplant. He also had surgery for pancreatic cancer in 2004.

“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.”

“Steve’s extraordinary vision and leadership saved Apple and guided it to its position as the world’s most innovative and valuable technology company,” CNN reported Apple board member Art Levinson as saying.  “In his new role as chairman of the board, Steve will continue to serve Apple with his unique insights, creativity and inspiration.”

Jobs co-founded Apple in 1976 with Steve Wozniak.

[CNN]