Apple co-founder and former chief executive Steve Jobs has died aged 56, the US technology company announced.
The company said in a statement: "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."
Mr Jobs had battled cancer in 2004 and underwent a liver transplant in 2009 after taking a leave of absence for unspecified health problems.
He took another leave of absence in January - his third since his health problems began - before resigning as CEO six weeks ago.
Mr Jobs became Apple's chairman and handed the CEO job over to his hand-picked successor, Tim Cook.
The news Apple fans and shareholders had been dreading came the day after the company unveiled its latest version of the iPhone, just one in a procession of devices that shaped technology and society while Jobs was running the company.
Australian Prime Minister Julia Gillard said she was saddened by Mr Jobs' death, calling him an "incredible global innovator" who "literally changed our world".
She added: "All of us would be touched every day by products that he was the creative genius behind."
Mr Jobs was brave enough to think differently, bold enough to believe he could change the world, and talented enough to do it.- Obama
US President Barack Obama hailed Apple co-founder Steve Jobs as one of America's greatest innovators and said the world had lost a visionary.
Mr Obama said Mr Jobs was "brave enough to think differently, bold enough to believe he could change the world, and talented enough to do it".
He added: "By building one of the planet's most successful companies from his garage, he exemplified the spirit of American ingenuity.
"By making computers personal and putting the internet in our pockets, he made the information revolution not only accessible, but intuitive and fun.
"And by turning his talents to storytelling, he has brought joy to millions of children and grown-ups alike."
Mr Obama went on: "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.
"Michelle and I send our thoughts and prayers to Steve's wife, Laurene, his family, and all those who loved him."