Steve Jobs, the CEO of Apple Inc. (AAPL), has taken medical leave to focus on his health. In his absence, Chief Operating Officer Tim Cook will be responsible for day to day operations.

The news has come at a time when Apple's iPhone has just been arrived at Verizon's network, and iPad 2 and iPhone 5 are rumored to be launched this year.

Jobs has sent the following email to all employees of Apple:

At my request, the board of directors has granted me a medical leave of absence so I can focus on my health. I will continue as CEO and be involved in major strategic decisions for the company.

I have asked Tim Cook to be responsible for all of Apple's day to day operations. I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011.

I love Apple so much and hope to be back as soon as I can. In the meantime, my family and I would deeply appreciate respect for our privacy.

Health Concerns

In recent times, Jobs' health concerns have been as well known as his company's products like iPhone and iPad.

In mid-2004, Jobs told his employees that he had been diagnosed with a cancerous tumor in his pancreas. The prognosis for pancreatic cancer is usually very grim; Jobs, however, stated that he had a rare, far less aggressive type known as islet cell neuroendocrine tumor. After initially resisting the idea of conventional medical intervention and embarking on a special diet to thwart the disease, Jobs underwent a pancreatic oduodenectomy (or Whipple procedure) in July 2004 that appeared to successfully remove the tumor. Jobs apparently did not require nor receive chemotherapy or radiation therapy. During Jobs' absence, Timothy Cook, head of worldwide sales and operations at Apple, ran the company.

In early August 2006, Jobs delivered the keynote for Apple's annual Worldwide Developers Conference (WWDC). His thin, almost gaunt appearance and unusually listless delivery, together with his choice to delegate significant portions of his keynote to other presenters, inspired a flurry of media and internet speculation about his health.

In contrast, according to an Ars Technica journal report, WWDC attendees who saw Jobs in person said he looked fine; following the keynote, an Apple spokesperson said that Steve's health is robust.

Two years later, similar concerns followed Jobs' 2008 WWDC keynote address. Apple officials stated Jobs was victim to a common bug and that he was taking antibiotics, while others surmised his cachectic appearance was due to the Whipple procedure.

During a July conference call discussing Apple earnings, participants responded to repeated questions about Steve Jobs' health by insisting that it was a private matter. Others, however, opined that shareholders had a right to know more, given Jobs' hands-on approach to running his company.

The New York Times published an article based on an off-the-record phone conversation with Jobs, noting that while his health issues have amounted to a good deal more than 'a common bug,' they weren't life-threatening and he doesn't have a recurrence of cancer.

On August 28, 2008, Bloomberg mistakenly published a 2500-word obituary of Jobs in its corporate news service, containing blank spaces for his age and cause of death. Although the error was promptly rectified, many news carriers and blogs reported on it, intensifying rumors concerning Jobs' health.

Jobs responded at Apple's September 2008 Let's Rock keynote by quoting Mark Twain: Reports of my death are greatly exaggerated; at a subsequent media event, Jobs concluded his presentation with a slide reading 110 / 70, referring to his blood pressure, stating he would not address further questions about his health.

On December 16, 2008, Apple announced that marketing vice-president Phil Schiller would deliver the company's final keynote address at the Macworld Conference and Expo 2009, again reviving questions about Jobs' health.

In a statement given on January 5, 2009 on, Jobs said that he had been suffering from a hormone imbalance for several months. On January 14, 2009, in an internal Apple memo, Jobs wrote that in the previous week he had learned that my health-related issues are more complex than I originally thought and announced a six-month leave of absence until the end of June 2009 to allow him to better focus on his health. Tim Cook, who had previously acted as CEO in Jobs' 2004 absence, became acting CEO of Apple, with Jobs still involved with major strategic decisions.

In April 2009, Jobs underwent a liver transplant at Methodist University Hospital Transplant Institute in Memphis, Tennessee.

Steve Jobs and Apple

Steven Paul Jobs (born February 24, 1955) is an American business magnate and inventor. He is the co-founder and chief executive officer of Apple. Jobs also previously served as chief executive of Pixar Animation Studios; he became a member of the board of The Walt Disney Company in 2006, following the acquisition of Pixar by Disney. He was credited in the 1995 movie Toy Story as an executive producer.

In the late 1970s, Jobs, with Apple co-founder Steve Wozniak, Mike Markkula, and others, designed, developed, and marketed one of the first commercially successful lines of personal computers, the Apple II series. In the early 1980s, Jobs was among the first to see the commercial potential of the mouse-driven graphical user interface which led to the creation of the Macintosh.

After losing a power struggle with the board of directors in 1984, Jobs resigned from Apple and founded NeXT, a computer platform development company specializing in the higher education and business markets. Apple's subsequent 1996 buyout of NeXT brought Jobs back to the company he co-founded, and he has served as its CEO since 1997.

In 1986, he acquired the computer graphics division of Lucasfilm Ltd which was spun off as Pixar Animation Studios. He remained CEO and majority shareholder at 50.1% until its acquisition by The Walt Disney company in 2006. Consequently Jobs became Disney's largest individual shareholder at 7% and a member of Disney's Board of Directors.

Jobs' history in business has contributed much to the symbolic image of the idiosyncratic, individualistic Silicon Valley entrepreneur, emphasizing the importance of design and understanding the crucial role aesthetics play in public appeal. His work driving forward the development of products that are both functional and elegant has earned him a devoted following.

Jobs is listed as either primary inventor or co-inventor in over 230 awarded patents or patent applications related to a range of technologies from actual computer and portable devices to user interfaces (including touch-based), speakers, keyboards, power adapters, staircases, clasps, sleeves, lanyards and packages.

As of October 2009, Jobs owned more than 5 million shares of Apple, most of which was granted in 2003 when Jobs was given 10 million shares. He also owned 138 million shares of Disney, which he received in exchange for Disney's acquisition of Pixar.

Forbes estimated his net wealth at $5.1 billion in 2009, making him the 43rd wealthiest American. Jobs has been criticized for his lack of public philanthropy despite his wealth, particularly in recent years as other billionaires (such as Bill Gates and Warren Buffet) have pledged significant portions of their fortunes to charity.

Shares of Cupertino, California-based Apple could open lower on Tuesday following rising concerns over Jobs' health. The stock closed Friday's regular trading session on Nasdaq at $348.48.