Apple Inc. shares were down as much as 2 percent in early U.S. trading Thursday, after the company's co-founder and chief executive officer Steve Jobs resigned for health reasons on Wednesday.

Jobs said he could no longer meet the “duties and expectations” of the position. Jobs has been fighting pancreatic cancer since 2003, received a liver transplant in 2009, and has been on medical leave since January.

In a note on its website, Apple said Jobs had “saved” Apple with “extraordinary vision and leadership.” Jobs has been elected as chairman of the board of directors. Company officials say he will continue to contribute “unique insights, creativity and inspiration.”

Tim Cook will take over as Apple's new top executive at the recommendation of Jobs. Cook had previously served as the company's chief operating officer. Apple's board said Cook has demonstrated “remarkable talent and sound judgment in everything he does” in the 13 years he has worked for the firm.

Apple is now the world's most valuable technology company, but in the 1990s, the company nearly went bankrupt. Its fortunes were transformed when it shifted its focus away from being a personal computer manufacturer into a company producing the trendy iPhone and the iPad tablet for audio-visual media.