Updated: Apple co-founder Steve Jobs died Wednesday evening, ending a battle with cancer that was both public and stubbornly private. Jobs stepped down in August after several years as his health declined. News of his death comes just one day after his successor, Tim Cook, hosted the introduction of the iPhone 4S. Though Jobs couldn't completely avoid discussion of his illness, he resisted calls for him to release details for the benefit of investors and the media. Say Reuters:

Job's health had been a controversial topic for years. His battle with cancer had been a deep concern to Apple fans, investors and the company's board alike. In past years, even board members have confided to friends their concern that Jobs, in his quest for privacy, wasn't being forthcoming enough with directors about the true condition of his health.

Reuters also recalled Jobs' commencement speech at Stanford, where he said:

"Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose. You are already naked. There is no reason not to follow your heart."

President Obama released a statement saying, in part:

Steve was fond of saying that he lived every day like it was his last.  Because he did, he transformed our lives, redefined entire industries, and achieved one of the rarest feats in human history: he changed the way each of us sees the world. The world has lost a visionary. And there may be no greater tribute to Steve’s success than the fact that much of the world learned of his passing on a device he invented.

Jobs's successor, Tim Cook, sent this message to Apple employees:

Team, I have some very sad news to share with all of you. Steve passed away earlier today. Apple has lost a visionary and creative genius, and the world has lost an amazing human being. Those of us who have been fortunate enough to know and work with Steve have lost a dear friend and an inspiring mentor. Steve leaves behind a company that only he could have built, and his spirit will forever be the foundation of Apple. We are planning a celebration of Steve’s extraordinary life for Apple employees that will take place soon. If you would like to share your thoughts, memories and condolences in the interim, you can simply email rememberingsteve@apple.com. No words can adequately express our sadness at Steve’s death or our gratitude for the opportunity to work with him. We will honor his memory by dedicating ourselves to continuing the work he loved so much. Tim

Venturebeat posted this picture of flags lowered to half-staff at Apple's headquarters. David Gewirtz of ZDnet has a lovely remembrance here. For more reactions from around the tech world, click here. At Bnet, Constantine von Hoffman reminds us that Jobs also founded Pixar, whose approach to animation and movie-making has been revolutionary in and of itself.

His family said:

Steve died peacefully today surrounded by his family. In his public life, Steve was known as a visionary; in his private life, he cherished his family. We are thankful to the many people who have shared their wishes and prayers during the last year of Steve’s illness; a website will be provided for those who wish to offer tributes and memories. We are grateful for the support and kindness of those who share our feelings for Steve. We know many of you will mourn with us, and we ask that you respect our privacy during our time of grief.

Apple's board of directors released this statement:

We are deeply saddened to announce that Steve Jobs passed away today. Steve's brilliance, passion and energy were the source of countless innovations that enrich and improve all of our lives. The world is immeasurably better because of Steve. His greatest love was for his wife, Laurene, and his family. Our hearts go out to them and to all who were touched by his extraordinary gifts.