Apple Inc. co-founder Steve Jobs resigned Wednesday as chief executive officer. He was succeeded by chief operating officer and right-hand man Tim Cook but will continue to serve as chairman of the board.

Jobs has been on medical leave since Jan. 17, fighting a rare form of pancreatic cancer. His often-gaunt appearance has sparked questions about his health and his ability to continue, Reuters reported.

"The announcement has ramifications not only for the future of Apple's product line, but also over whether it can continue to maintain its position in the market, and sparks questions over whether Cook will be able to introduce his own vision to the company or simply continue living under Jobs' shadow," said Patrick Stafford, editor of TechCompany.

Industry experts do not expect Jobs' resignation to cause an upheaval in Apple's product-launch roadmap, which could include a new iPhone in September. But company shares still fall about 7 percent hours after Job's announcement.

"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," he said in his letter of resignation posted in the Apple Web site.

In March, Jobs was still able to unveil the latest version of the iPad. He also attended a dinner hosted by President Barack Obama for technology leaders in Silicon Valley.

Considered as the heart and soul of Apple Inc., Jobs ends an era by resigning.

Jobs was a college dropout, a Buddhist, and a son of adoptive parents. In the 1970s, he co-founded Apple Computer with friend Steve Wozniak in the Jobs family garage in Silicon Valley. They introduced the Apple I computer, but it was the Apple II that became a big success and launched Job's career in the PC industry and made him a multimillionaire.

In 1985, Jobs left the company due to problems with Apple's board and management. He founded the computer company NeXT, which was purchased by Apple in 1997. This brought Jobs back to the company, and he became CEO in 2000.

Analysts continue to be positive about the changes in Apple.

"Steve's extraordinary vision and leadership saved Apple and guided it to its position as the world's most innovative and valuable technology company," said Art Levinson, chairman of Genentech, on behalf of Apple's board. "Steve has made countless contributions to Apple's success, and he has attracted and inspired Apple's immensely creative employees and world class executive team. In his new role as chairman of the board, Steve will continue to serve Apple with his unique insights, creativity and inspiration."

"The board has complete confidence that Tim is the right person to be our next CEO," added Levinson. "Tim's 13 years of service to Apple have been marked by outstanding performance, and he has demonstrated remarkable talent and sound judgment in everything he does."