Jobs has wrestled with cancer in recent years and took an indefinite leave of absence starting in January, saying he wanted to focus on his health. In its statement, Apple did not say why Jobs was resigning as CEO or make any mention of his health. Jobs submitted his resignation Wednesday and "strongly recommend[ed]" that Cook be elected CEO, Apple said.

Jobs has been elected chairman of Apple's board, effective immediately, and Cook has been made a board member, the statement said.

"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 and an Apple board member, said in a statement.

He said that the board had full confidence in Cook, who has led the company during both of Jobs' leaves of absence. As Apple's chairman, Jobs will continue to serve Apple "with his unique insights, creativity and inspiration." Levinson said.

Jobs is "an icon and what he's done with Apple is something probably unprecedented in business," said IDC analyst Al Hilwa. "It will be a case study in business school books for decades."