Apple boss Steve Jobs sparked new speculation about his health after announcing a second medical leave of absence in two years.
In the last decade, Mr Jobs, 55, the charismatic frontman for the company that overturned the smartphone industry and invented a new category of tablet computers, has survived a rare but curable form of pancreatic cancer and undergone a liver transplant.
The news that he will again step down from his day-to-day role raises serious questions about the CEO's health.
But analysts believe the company he shepherded from garage start-up to a 65 billion dollar (£42bn) technology trendsetter is in good hands with the current slate of talented executives - even as Apple, now the Silicon Valley player to beat, faces increasing competition.
Chief executive Mr Jobs has played the role of industry oracle, seeming to know what consumers want even before they do. He is also known as a demanding and hands-on leader who is involved in even the smallest details of product development.
Investors have pinned much of their faith in the company on Jobs himself, sending shares tumbling on every bit of news or rumour of his ailing health.
For now, very little is known about Mr Jobs' current condition. Apple did not provide any information beyond a six-sentence note from Mr Jobs to employees announcing his leave, leaving unanswered questions about whether he is acutely ill, whether the leave is related to his 2009 liver transplant or whether he is at home or in hospital.
Unlike Mr Jobs' 2009 leave of absence, when he vowed to return to work in just under six months, he did not say in the note made public yesterday how long he would be on leave this time. He said he would continue as CEO and be involved in major decisions.
Chief operating officer Tim Cook will be responsible for all day-to-day operations.
"I love Apple so much and hope to be back as soon as I can," Mr Jobs wrote. "In the meantime, my family and I would deeply appreciate respect for our privacy."