Apple chief executive officer Steve Jobs resigned Wednesday, effective immediately. Chief operating officer Tim Cook will take over, as per Jobs’s recommendation. Jobs, who cofounded the company in his garage, has been elected chairman of the board. Jobs, 56, a pancreatic-cancer survivor, has been on medical leave from Apple since January for an undisclosed medical condition. In a letter to the board he said: "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." In the immediate aftermath of the announcement, Apple shares fell 5 percent.