With Steve Jobs? resignation today as CEO of Apple Inc., the man who changed the face of computing and then went on to repeat the performance with mobile leaves the field just when smartphones and tablets are beginning to turn the worlds of commerce, content, communication and marketing upside down.

While Mr. Jobs will still maintain ties with Apple as its newly elected chairman of the board, his active input on the creative design process and product advertising will be missed. Suffering serious ailments over the last few years, Mr. Jobs? second departure at Apple?s helm was unthinkable but expected, especially since his picked successor as CEO, Tim Cook, quite ably ran the shop while his boss was out on sick leave.

?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, said in a statement 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,? he said. ?In his new role as chairman of the board, Steve will continue to serve Apple with his unique insights, creativity and inspiration.?

New era begins
The jury is out whether Mr. Jobs? departure as CEO will affect Apple?s leadership in mobile devices, but it could give an opening to rivals such as Google, Microsoft, Research In Motion, Nokia, Samsung and LG to claw back market share in the absence of the one man who could single-handedly sway consumers and markets.

Mr. Jobs in March entered the Mobile Hall of Fame ? Mobile Marketer?s highest honor to an individual who made the most difference in mobile ? for his contributions to the post-PC era.

Not many people are aware that Mr. Jobs is also one of the single largest shareholders in Walt Disney Co., home to Mickey Mouse.

In his successor, Mr. Jobs has found someone who can carry the Apple torch with the same creative intensity, design focus and marketing savvy that make Apple products such as the MacBook, iMac, iPhone, iPod, iPad, iTunes and iBooks game-changers in their respective categories.

Mr. Cook has subbed for Mr. Jobs on a couple of occasions, including the last few months.

A 13-year veteran of Apple, Mr. Cook was most recently chief operating officer. He was responsible for worldwide sales and operations, with oversight for end-to-end management of Apple?s supply chain, sales activities and service and support.   

Mr. Cook also ran Apple?s Macintosh division and helped develop strategic reseller and supplier relationships.

With his departure, Mr. Jobs follows the example of rival tech executive Bill Gates to the chairman?s post.

Mr. Gates yielded the Microsoft CEO?s job a decade ago to Steve Ballmer, whose tenure has seen mixed results for the company, albeit keeping it highly profitable.

Goodbye letter
Here is the letter that Mr. Jobs released at 6:35 p.m. ET on Aug. 24 to the Apple board and the public:

To the Apple Board of Directors and the Apple Community:

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.

I hereby resign as CEO of Apple. I would like to serve, if the Board sees fit, as Chairman of the Board, director and Apple employee.

As far as my successor goes, I strongly recommend that we execute our succession plan and name Tim Cook as CEO of Apple.

I believe Apple?s brightest and most innovative days are ahead of it. And I look forward to watching and contributing to its success in a new role.

I have made some of the best friends of my life at Apple, and I thank you all for the many years of being able to work alongside you.

Steve